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The International Joint AIRAPT-22 & HPCJ-50 Conference was held in Odaiba, Tokyo, on 26–31 July 2009. About 480 scientists from 24 countries attended the conference and 464 papers, including 3 plenary lectures, 39 invited talks, and 156 oral presentations, were presented. It is my great pleasure to present this proceedings volume, which is based on the high quality scientific works presented at the conference.

The International AIRAPT conference has been held every two years in various countries around the world since 1965, while High Pressure Conference of Japan (HPCJ) has been held annually since 1959 in various Japanese cities. Pressure is a fundamental parameter to control the property of matter. As a result, both AIRAPT and HPCJ have become highly multidisciplinary, and cover Physics, Chemistry, Materials Science, Earth and Planetary Sciences, Biosciences, Food Science, and Technology. Although each discipline has a unique target, they all have high-pressure research in common. This proceedings volume includes about 200 papers of state-of-the-art studies from numerous fields. I hope this proceedings volume provides excellent pieces of information in various fields to further advance high-pressure research.

Takehiko Yagi Conference Chairman Institute for Solid State Physics The University of Tokyo 7 December 2009

Participants at the conference venue, Tokyo International Exchange Center, Odaiba, Tokyo, Japan.

Editor in ChiefTAKEMURA Kenichi National Institute for Materials Science, Japan

Editorial boardTadashi KONDO Osaka University, Japan Hitoshi MATSUKI The University of Tokushima, Japan Nobuyuki MATUBAYASI Kyoto University, Japan Yoshihisa MORI Okayama University of Science, Japan Osamu OHTAKA Osaka University, Japan Chihiro SEKINE Muroran Institute of Technology, Japan

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Pressure-induced phase transitions of Zn(OH)₂ were investigated under hydrostatic condition at room temperature by an in-situ X-ray powder diffraction method and a visible observation method for a single-crystalline specimen. Two phase transitions were observed in the pressure range up to 4GPa. The first transition occurred at 1.1 GPa and it was a quick single crystal – single crystal transition. The high-pressure phase 1 with a tetragonal α-cristobalite-related structure was stable up to 2.1GPa. The coordination number of zinc atoms was 4+2. The second phase transition was observed above 2.1GPa. The high-pressure phase 2 was quenchable to ambient condition. The crystal structure has not been determined yet because the X-ray powder diffraction pattern was too broad to be even indexed. Comparison of polymorphs in Zn(OH)₂ suggests that the volume per chemical formula of the high-pressure phase 2 is in 40.0 – 44.5 ų at 2.1 GPa and room temperature and that the coordination number of zinc atoms in the phase is probably 4+2 or 5.

We have collected synchrotron X-ray diffraction patterns of FeCO₃-siderite after or in-situ laser heating at high pressures to 66 GPa. Diffraction peaks of FeCO₃ in all diffraction patterns obtained can be indexed as a trigonal cell. However, calculated cell volumes show an abrupt decrease (about 6.5%) between 47 and 50 GPa at room temperature. This abrupt change of the cell volume on FeCO₃ is possibly due to a pressure-induced spin transition of ferrous Fe (HS: high-spin → LS: low-spin). Because cell parameters obtained at high temperature and at pressures above 50 GPa suggest HS state rather than LS state, the Clapeyron slope of the HS-to-LS transition of FeCO₃ should be positive.

Lanthanide sesquioxides (Ln₂O₃) display three stable solid phases as a function of temperature. It has been assumed that Y₂O₃ should display similar crystal structures and phase transitions as other Ln₂O₃. Recently a new phase transition sequence was reported for Y₂O₃, contradicting earlier studies. In this work Y₂O₃ was found to have the same phase transition sequence as other lanthanide sesquioxides (Ln₂O₃). Additionally, in this study increasing external pressure has been found to have a similar effect to increasing temperature on crystal structure in Y₂O₃. At room temperature the first pressure-induced phase transition occured at ~13 GPa, in which the symmetry changed from cubic to monoclinic symmetry. The symmetry then changed from monoclinic to hexagonal at 24.5 GPa. The sequence of phase transitions was not reversible upon pressure release. With decreasing pressure only a single phase transition occurred, from hexagonal to monoclinic symmetry.

By use of synchrotron radiation, powder x-ray diffraction of SmBi with a NaCl-type structure has been studied up to 30 GPa at room temperature. A first-order phase transition began to occur at around 16.2 GPa. SmBi transformed from the NaCl-type (B1) to the tetragonal (distorted CsCl-type) structure with the volume collapse of about 8.2 % at around 18.3 GPa. Crystal data of the single phase are a = 3.775(5) Å, c = 3.25 (2) Å, c/a = 0.86 and V = 46.4 (3) ų at 20.3 GPa. The high-pressure form of SmBi is isostructural with that of SmAs. A bulk modulus of SmBi was estimated from the volume vs. pressure curve fitted by a Birch equation of state. The bulk modulus (B₀) and its pressure derivative (B₀') are 68 ± 3 GPa and 3.9 ± 0.3, respectively. The transition pressure and the bulk modulus of SmBi are larger than those of CeBi and PrBi. The structural high-pressure behaviour for SmX (X = P, As, Sb and Bi) is discussed. The structural phase transition of LaBi and NdBi occurred at around 11.5 GPa and 16.8 GPa, respectively. The transition pressures of LnBi (Ln = La, Ce, Pr, Nd and Sm) decreased with increasing lattice constant.

Using synchrotron radiation, the x-ray diffraction of the binary, unfilled-skutterudite compound TSb₃ (T=Co, Rh and Ir) has been studied under high pressure employing a diamond anvil cell up to 43 GPa. We have verified the pressure-induced irreversible isosymmetric structural change of CoSb₃, which was reported recently. Furthermore, we have observed that isostructural compounds RhSb₃ and IrSb₃ also show a similar pressure-induced structural change. The origin of the anomalous behavior for TSb₃ is discussed based on a simulation for a pressure-induced Sb self-insertion reaction model.

The rare-earth and actinide based intermetallics are endowed with exotic physical and chemical properties due to the presence of idiosyncratic f-electrons in these systems. These properties exhibit interesting changes under the action of various thermodynamic fields and hence continue to be a subject of extensive research. For instance, under pressure, the nature of f-electrons can be changed from localized to itinerant, leading to a variety of changes in their structural, physical and chemical properties. During the last one and half decade, we have carried out extensive research on the structural stability and phase transition behaviour of the aluminides and gallides of these f-electron based systems using a unique combination of Guinier diffractometer and diamond anvil cell. To bring out the correlations between the structural stability and phase transition behaviour with their electronic structure, we have also carried out electronic structure calculations as a function of reduced volume. In this talk, we have presented some of our studies on the AB₂ type actinide and rare-earth based intermetallics, elaborated on the trends seen in the structural behaviour and correlated with their electronic structure.

We report on the pressure dependence of the order of ferromagnetic (FM) to paramagnetic (PM) phase transition in (Sm_0.7Nd_0.3)_0.52Sr_0.48MnO₃ single crystal. At ambient condition, the system exhibits clear evidences of first-order FM-PM phase transition at (Tc ≈ 146 K). The application of pressure (P = 12.1 kbar) makes the FM transition second-order in nature with Tc≈ 176K.

The structural phase transformations in the chalcopyrite semiconductor AgInTe₂ have been studied up to 10 GPa on both pressure increase and decrease. The experiments were conducted using angle-dispersive X-ray diffraction with synchrotron radiation and an image plate. The diffraction patterns of AgInTe₂ at ambient pressure reveal two coexisting phases: the first has the chalcopyrite structure while the second has a zincblende-like structure. On pressure increase both phases transformed at 3-4 GPa to a cation-disordered orthorhombic structure with spacegroup Cmcm. On pressure decrease, the chalcopyrite phase started to reappear at 0.55 GPa, and the Cmcm phase disappeared completely at ambient pressure.

The high-pressure evolution of the cubic perovskite NH₄MnCl₃ has been studied in the 0-6 GPa range by angle-dispersive x-ray diffraction. A structural phase transition has been found at low pressure (P_C = 0.4 GPa), in agreement with previous reports. The high-pressure phase has been refined in the tetragonal P4/mbm and orthorhombic Pbnm space groups. In either case, the structure can be described in terms of a tilted perovskite model (one tilt a⁰a⁰c⁺and two tilts a⁺b⁻b⁻, respectively). The average tilting under pressure has been estimated from the lattice parameters. The P-V relation has been fitted by a Murnaghan Equation-of-State with K₀ = 29(2) GPa and K'₀ = 9(1).

Compression of PrN yields a phase transformation to a tetragonal structure with ~8.8 % volume collapse at ~40 GPa at ambient temperature. A refinement reveals a distorted CsCl-like structure for the high pressure phase PrN(II), which is different from the high pressure phases seen among other lanthanide monopnictides. The space group of the new structure is P4/nmm (#129) with Pr in the 2c(0,1/2,0.3546) and N in the 2a(0,0,0) positions. PrN(II) persists to 85 GPa.

The high pressure X-ray diffraction study of B₄C was carried out by using the synchrotron radiation source. The ambient crystal structure remained stable to the highest pressure 126 GPa, and the pressure induced amorphization did not occurs. The c/a ratio decreased with increasing pressure that means the apex angle of the rhombohedron increases with increasing pressure. The bulk modulus was determined by the Birch-Murnaghan's equation to be 305.8 GPa.

The crystallographic structure of HfIr₃ was studied as a function of pressure using X-ray diffraction technique. No phase transition was observed up to a pressure of 27.6 GPa, with a total volume contraction of V/V0 ≊ 0.92. The bulk modulus value, calculated from the X-ray experimental data and from the sound-velocity technique, are B=279±4 and 297.9±2.5 GPa, respectively. The relatively high value of the bulk modulus, combined with a high density value of ρ=20564 kg/m³, and a high hardness value of 6.05±0.26 GPa, positions this compound as a possible application for extreme environments. The electronic structure of HfIr₃, studied with the full potential linearized augmented plane calculations technique, indicates that the main cause for the unusual properties of this compound are the Iridium unfilled 5d-shell of this atom.

The phase stability of a commercial purity (Ti-CP), high purity (Ti-HP) and Ti-6Al-4V alloy were investigated in a diamond anvil cell up to 32 GPa and 298 K using a polychromatic X-ray beam. The Ti-CP and Ti-HP shown the same HCP (c/a~0.632) to Hexagonal (c/a~1.63) non reversible martensitic transition at about 9 GPa. The as received Ti-6Al-4V shows a very low relative volume fraction β-Ti / α-Ti. No phase changes were observed in the Ti-6Al-4V alloy in the pressure range of this study. The α phase of the Ti-6Al-4V shows monotonic volume cell pressure dependence. This volume change is reversible and non-hysteretic. The cell of the a phase recovered its original volume when the pressure was released.

The pressure-volume relationship of Fe₇₂Pt₂₈ alloy was investigated at 300, 500, 700, 900, 1100, and 1300 K by performing energy-dispersive X-ray diffraction measurements using a white X-ray beam produced from synchrotron radiation at the High Energy Accelerator Organization, Japan. The pressure-volume relationship measurements were performed only along the decreasing the pressure path. Below 700 K and 3.5 GPa, the compressibility of Fe₇₂Pt₂₈ alloy increased with the pressure. Above 900 K, the pressure-volume relationship was almost linear. Further the temperature-volume relationship at high pressures was linear. An abrupt decrease in the volume or a thermal expansion coefficient anomaly, which was observed in the case of Fe₆₉Ni₃₁ alloy in previous experiments, was not observed in the case of Fe₇₂Pt₂₈ alloy,

Synchrotron X-ray diffraction study for solid CO₂ at 40–100 GPa and around 2,000 K has shown that the diffraction pattern of the high pressure phase CO₂-V is consistently interpreted in terms of a tetragonal uni_{_}t cell (Z = 4, a = 3.584 Å, c = 5.908 Å at 50GPa). A β-cristobalite structure (space group I2d) gives a good account of our data qualitatively. Isothermal molar volume (300K) of the CO₂-V in the present study is smaller than that indexed as a tridymite structure proposed by previous studies at any pressures.

We present both structural and vibrational (Raman) results of compressed xenon binary systems of He and H₂ to a maximum pressure of 142 GPa. In the He-Xe mixture 15% vol. Xe and balance He, we observe no evidence for van der Waals compound formation. Pure fcc Xe can be crystallised from the 2-phase Xe-He fluid at 0.6 GPa. The expected fcc-hcp transition is accompanied by extensive diffuse scattering and the emergence of hcp reflections at higher pressures. There is no apparent volume expansion of the measured Xe equation of state in helium indicating a near-zero (iso-structural) solubility of He in Xe. In the H₂-Xe system, X-ray diffraction revealed the presence of two solid-phase structures in a 15% by volume mixture, one of which was best indexed on an orthorhombic cell. Raman spectroscopic studies of both 15% and 7.5% Xe binary mixtures by volume in H₂, showed shifted vibron frequencies relative to the normal, pure (bulk) H-H stretch mode (vibron) that soften with pressure and appear to cross the pressure-frequency trajectory of the H₂ vibron. The 7.5 vol % Xe-H₂ mixture freezes at 5.3 GPa to a solid occupying the bulk of the available sample volume in the DAC, indicating a close-to-stoichiometric composition for one Xe-H₂ solid phase.

Powder x-ray diffraction experiments have been done on Ne up to 237 GPa at room temperature. Ne remains in the fcc phase up to the highest pressure. In order to observe the weak 200 reflection at ultrahigh pressures, we have used the tube-cross slit at the exit side of x-rays, which effectively reduced the scattered x-rays by the diamond anvil. The lattice parameters obtained from the 111 and 200 reflections significantly differ from each other, implying the existence of sizable uniaxial stress in Ne at ultrahigh pressures. On the basis of the calculated elastic constants of Ne at high pressures, we conclude that the 111 reflection is least affected by the uniaxial stress. The equation of state constructed from the 111 reflection agrees well with previous data.

Among three intermetallic compounds existing in Y-Mn system the YMn₂ and Y₆Mn₂₃ can easily form interstitial hydrides while for YMn₁₂ existence of hydride has never been reported. At moderate hydrogen pressure YMn₂ and Y₆Mn₂₃ transform into YMn₂H_4.5 and Y₆Mn₂₃H₂₅ respectively. At high hydrogen pressure the YMn₂ (C15 or C14 parent structure) forms a unique YMn₂H₆ (s.g. Fm3m) complex hydride of fluorite structure in which one Mn atom Mn(1) and Y randomly occupy the 8c sites while second manganese (Mn2) in position 4a forms complex anion with 6 hydrogen atoms located in positions 24e. Formation of YMn₂H₆ independently of the structure of parent phase (C14 or C15) as well as occupation of the same site (8c) by Y and Mn(1) atoms suggested that also Y₆Mn₂₃ and YMn₁₂ could transform into YMn₂H₆ – type hydride in which suitable number of Y atoms will be substituted by Mn(1) in the 8c positions. This assumption was confirmed by exposing R₆Mn₂₃ and RMn₁₂ to 1 GPa of hydrogen pressure at 100⁰C. Formation of (R_xMn_2−x)MnH₆ (where x = 18/29 or 3/13 for R₆Mn₂₃ and RMn₁₂ hydrides respectively) was confirmed by XRD. Hydrogen concentration in both R₆Mn₂₃ and RMn₁₂ based hydrides reached H/Me = 2 thus value two times higher than in R₆Mn₂₃H₂₅.

Synchrotron x-ray powder diffraction studies on an icosahedral Cd-Yb quasicrystal (iCd-Yb), its crystalline approximant of Cd₆Yb (cCd-Yb) and the related Cd₂₅Eu₄ (cCd-Eu) material were performed under pressures of up to about 40 GPa at room temperature. The icosahedral lattice of the atomic cluster in iCd-Yb and the bcc lattices in cCd-Yb and cCd-Eu were found to be stable under pressure. Although the Tsai-type atomic cluster can possibly be distorted in various ways, low-symmetry distortion modes do not seem to develop even at high pressure. It is considered that the cluster structure of centrosymmetric dense atomic packing prevented low-symmetry distortions and consequently provided the cluster lattice stability. The bulk moduli were also determined to be B₀(iCd-Yb) = 49.2(3) GPa, B₀(cCd-Yb) = 46.1(7) GPa and B₀(cCd-Eu) = 49.6(3) GPa, which were much lower than the typical reported values for other quasicrystalline alloys.

The alkali fulleride Rb₄C₆₀ has been investigated by studies of the resistance and by Raman spectroscopy under pressures up to 2 GPa and 13 GPa, respectively. Our data show a reversible phase separation into metallic Rb₃C₆₀ and Rb₆C₆₀ at pressures above 1 GPa. The reversibility indicates that the phase separation primarily occurs on the nanometer length scale. The data explain several puzzling results reported in the recent literature.

Novel approaches to the collection and treatment of total x-ray scattering using high energy (> 65 keV) x-ray beams and area detectors allow in situ studies of unprecedented precision to be performed on nano-crystalline (n) and glassy materials at extremes of pressure (p) and temperature (T). Gradual structural transitions in glasses, liquids and nano-materials occurring via continuous changes in density, or involving phases related by pseudo symmetry are inherently difficult to identify due to their disordered nature. In such cases supplementary physical measurements along with modeling of the pair distribution function (PDF) provide powerful constraints on the possible models for the transition. Examples include transitions from n-FeS with a mackinawite-like structure to high p forms with structures related to NiAs structure-type. The distinction between the various high p models – MnP-type, troilite, FeS-III related or mixtures of these phases – is subtle; great care needs to be exercised in refining structure models to fit the observed data. Acoustic techniques are particularly valuable in identifying high p phase transitions in glasses, since measured changes in compressional velocities relate to density changes in the glass while shear waves provide an insight into network rigidity.

Time-resolved two-dimensional X-ray diffraction method has been applied to observe kinetic properties of polycrystalline high-pressure ices in diamond anvil cell. The relationships between the number of diffraction spots and the number of grains per radiated volume were calibrated at several beamlines of SPring-8 and Photon Factory. Based on the relationships, we examined kinetics of grain growth in ice VI and VII, and kinetics of the ice VI-VII and VI-VIII transformations, from the evolution of the number of diffraction spots. Preliminary results on these kinetic experiments are presented in this paper.

J-PARC, a high-intensity proton accelerator facility in Japan, has been open to public use since December 2008, and various high-pressure experiments are expected to be conducted using its high-intensity pulsed neutron beam. The first test experiment using a Paris-Edinburgh (PE) press was performed with the Engineering Materials Diffractometer "TAKUMI". The powder diffractions of standard samples in the press were successfully obtained using two different geometries (vertical scattering geometry and horizontal scattering geometry). Although the signal was weak and there are still many issues to be solved, it has been confirmed that in situ high-pressure neutron powder diffraction is feasible at J-PARC.

To reveal hydrogen-metal interaction in metal hydride systems with high hydrogen density, we have constructed the high-pressure device for neutron diffraction at total scattering spectrometer NOVA in J-PARC. The device consists of the Paris-Edinburgh press, the alignment stages, the automatically regulated oil pump system and the temperature control system. By using this device, diffraction data are expected to be taken at pressures above 20 GPa over wide Q-range of 1-40A⁻¹ with the resolution of ΔQ/Q~0.6 %, which enables us to determine hydrogen positions in high hydrogen-density materials in the real-space resolution of 0.16A.

The powder diffractometer dedicated to high-pressure experiments (PLANET) is now being constructed on BL11 at the spallation neutron source of J-PARC. PLANET aims to study structures of hydrogen-bearing materials including dense hydrous minerals of the Earth's deep interior, magmas and light element liquids. The instrument will realize diffraction and radiography experiments for powder and liquid/glass samples at high pressures up to 20 GPa and 2000 K. It covers d spacing from 0.2 Å to 4.1 Å at 90° bank within the first frame. The design and performance of PLANET have been evaluated using Monte Carlo simulations.

A new high-pressure apparatus has been developed for studies of synchrotron radiation-based X-ray microtomography at SPring-8 of Japan. The high pressure tomography apparatus at SPring-8 is a compact hydraulic press with a 0.8 MN capacity and is equipped with an opposed anvil device. It has two wide windows for X-ray access with a 160-degree opening in the equatorial plane to the compression axis. Radiographs are acquired over 180 degree rotation for reconstruction of 3D image, in which some shadows occur, because the press frame blocks a 20-degree angular region. 3D tomography image computed from radiographs obtained using the high pressure tomography apparatus has a reasonably good quality enough to measure physical properties of materials.

We have demonstrated the feasibility of a two-dimensional angle-dispersive x-ray diffraction (2D-ADXD) measurement system using a Kawai-type multianvil press at SPring-8. By taking advantage of the x-ray-transparent anvil and energy-dispersive x-ray diffraction (EDXD) techniques, high-pressure 2D-ADXD measurements of KCl were performed up to 9.9 GPa. Entire Debye-Scherrer rings were obtained, and the B1-B2 phase change of KCl was clearly observed at 2.3 GPa. The developed 2D-ADXD measurement system enabled us to obtain enough high-quality diffraction data to precisely determine and refine the structure of KCl at high-pressure.

In situ falling-sphere technique viscosity measurements in a DIA-type multi-anvil apparatus – MAX80 at beamline F2.1 at DESY / HASYLAB, Hamburg, Germany – have been performed. The viscosity was measured following Stokes law by evaluation of X-radiography sequences taken by a CCD-camera. Powdered basalt, dacite, and diabase samples were measured at pressures of 0.5 and 1 GPa and temperatures of 1890 K. After pressurization the temperature produced by an internal graphite heater was increased up to sample melting observed by X-ray diffraction and X-radiography. The results cover a data range from 3.5 Pa s (basalt at 1 GPa) and 195.5 Pa s (diabase at 0,5 GPa) and are in good agreement with published data.

We present plans for the new Extreme Conditions Beamline at PETRA III, DESY, Germany. The beamline is being designed and built with the specific goal to explore time resolved high-pressure and -temperature x-ray diffraction experiments in the dynamic and laser heated diamond anvil cell. Within we discuss the conceptual design of the optical components and experimental setup to conduct monochromatic high-pressure powder diffraction experiments in the sub-second time regime.

Local geometry and electronic states of octahedrally coordinated Mn ions in orthorhombic DyMnO₃ have been studied by partial-fluorescence-yield spin-selective x-ray absorption spectroscopy and in-situ Raman scattering. As evidenced in absorption near-edge structure and Raman spectra, the external pressure alleviates the MnO₆ octahedral distortion and Jahn-Teller effect with enhanced octahedral tilt.

We have measured the electrical resistivity of CeZn₃P₃ single crystals under pressure up to 19 GPa for temperature down to 0.4 K. At ambient pressure, the electrical resistivity shows a semiconducting behavior with an energy gap E_g ~ 1800 K. We have found that the E_g monotonically decreases with increasing pressure, and possibly disappears at around 20 GPa.

A filled skutterudite La_0.48Rh₄As₁₂ was synthesized at 4 GPa and 1220 K. La_0.48Rh₄As₁₂ is a semiconductor with a energy gap of 0.03 eV at ambient pressure. Electrical resistance measurements at low temperatures and high pressures have indicated that La_0.48Rh₄As₁₂ is a semiconductor even at 20.0 GPa although a temperature change in the resistivity becomes small with pressure.

We investigate galvanomagnetic effects near the insulator-metal transition induced by pressure in Pb_1−xGe_xTe (x=0.10, 0.13) alloys doped with chromium (4.2≤T≤300 K, B≤8 T). We observe nonlinearity in the magnetic field dependencies of Hall voltage and peaks of anomalous scattering in the temperature dependencies of resistivity. These are due to the conductivity via chromium impurity band and to the structural phase transition from the cubic NaCl phase to the rhombohedral GeTe phase. Magnetic field dependencies of the Hall coefficient R_H(B) are calculated in the framework of two-band conduction model. The main parameters of charge carriers are determined. Pressure dependencies of the critical phase transition temperature are obtained.

Of the 52 known elemental superconductors among the 92 naturally occurring elements in the periodic table, fully 22 only become superconducting under sufficiently high pressure. In the rare-earth metals, the strong local magnetic moments originating from the 4f shell suppress superconductivity. For Eu, however, Johansson and Rosengren have suggested that sufficiently high pressures should promote one of its 4f electrons into the conduction band, changing Eu from a strongly magnetic (J=7/2) 4f⁷-state into a weak Van Vleck paramagnetic (J=0) 4f⁶-state, thus opening the door for superconductivity, as in Am (5f⁶). We report that Eu becomes superconducting above 1.8 K for pressures exceeding 80 GPa, T_c increasing linearly with pressure to 142 GPa at the rate +15 mK/GPa. Eu thus becomes the 53rd elemental superconductor in the periodic table. Synchrotron x-ray diffraction studies to 92 GPa at ambient temperature reveal four structural phase transitions.

Pressure dependence of the superconducting transition temperature T_c has been investigated in YbGa_1.1Si_0.9, which is the AlB₂-type layered superconductor with T_c = 2.4 K. The electrical resistivity measurements were carried out under hydrostatic pressure up to 2.5 GPa using a piston-cylinder type pressure cell. With increasing pressure, the T_c of YbGa_1.1Si_0.9 decreases from 2.4 K to 1.1 K at 2.5 GPa with a pressure derivative of T_c, dT_c/dP, of – 0.78 K/GPa. This negative pressure derivative of T_c is similar to the other superconducting AlB₂-type silicides. The relative pressure derivative of T_c, dlnT_c/dP, for YbGa_1.1Si_0.9 is – 0.33 GPa⁻¹, which is about ten times larger than those for other layered superconductors.

We have investigated the pressure dependence of superconducting transition temperature T_c of Bi₂Te₃ through electrical resistance measurement under high pressure up to 13 GPa. The value of zero-resistance critical-temperature T_c^zero is 2.7 K at 9.0 GPa. Pressurization up to 11 GPa reduces the T_c^zero. However the pressurization at 13 GPa causes sudden enhancement of T_c^zero, which is obtained to be 3.7 K. The onset temperature of superconducting transition T_c^onset shows the positive pressure dependence under pressure above 10 GPa. The value of T_c^onset is obtained to be 5.0 K at 13 GPa. The sharp increase of T_c^zero and the positive pressure dependence of T_c^onset suggest a presence of new superconducting phase.

Pressure dependence on superconducting transition temperature (T_c) has been investigated for iron-based superconductor LaFeAsO_1−xF_x, SmFeAsO_1−xF_x and Ca(Fe_1−xCo_x)AsF. The T_c increases largely for LaFeAsO_1−xF_x with a small increase of pressure, and decreases with further compression. In SmFeAsO_1−xF_x the T_c decreases with increasing pressure. The increase of T_c in LaFeAsO_1−xF_x seems to be related to the suppression of magnetic ordering phase. Pressure-induced superconductivity was observed for these materials. The common features on 1111 type superconductors are discussed.

CaRuO₃ post-perovskite which has quasi-two-dimensional lattice shows one dimensional antiferromagnetism such as Bonner-Fisher type above 400 K. The Néel temperature, T_N, is around 270 K.

Electrical resistivity ρ and thermopower S of Y_1−xR_xCo₂ (R=Gd, Tb, Dy, Ho and Er) Laves phase alloy systems were measured at temperatures from 1.5 K to 300 K in magnetic fields up to 15 T and under hydrostatic pressure up to 2 GPa. We show that there is a universal linear relation between the pressure and magnetic field derivatives of the resistivity, dρ/dP and dρ/dB, with gradient, determined by pressure derivative of the critical metamagnetic field of the cobalt 3d electron system. A similar scaling behavior was found for the thermopower dependencies on pressure and alloy composition.

The temperature dependence of magnetization (M) and resistivity (ρ) of La_1−xSr_xCoO₃(x=0.10, 0.33) single crystals have been analyzed. For x=0.10, the temperature dependence of field-cooled magnetization (M_FC) and zero-field-cooled magnetization (M_ZFC) is similar to that expected for a canonical spin-glass system. The thermal response of M_ZFC for x=0.33 indicates a glassy ferromagnetic state. We observe that the ferromagnetic transition temperature T_C decreases and ρ increases rapidly with increasing pressure (P) for the metallic sample (x=0.33), while the dependence of ρ on P for the insulating sample (x=0.10) is quite complicated; the pressure coefficient of resistivity (dρ/dT) is sensitive to temperature and applied pressure due to the strong interplay between the pressure-induced band broadening and spin-state transition phenomenon. dρ/dT is large and negative at low-pressure and low-temperature regime while small and positive at high pressures (P>5.4 GPa) and high temperatures (T>110 K).

We performed resistivity and zero-external-field (ZF) ⁷⁵As nuclear magnetic resonance (NMR) measurements of Ba_1−xK_xFe₂As₂ (x = 0 and 0.4) under high pressure. ZF ⁷⁵As NMR measurements revealed that the magnetic ordered state is robust against pressure. On the other hand, superconducting transition temperature T_c has a tendency to decrease monotonically under pressure. The spin-lattice relaxation rate 1/T₁ in antiferromagnetic and superconducting states suggests that the coexistence of the both states is not microscopic but is phase separated.

The excited state dynamics of Erbium(III) ions in perfluorinated compounds Er_xY_1−x[(p-CF₃-C₆F₄)₂PO₂]₃ has been studied using high pressure, over a range of temperatures. These fluorinated compounds have a long lifetime for the erbium ⁴I_13/2 → ⁴I_15/2 emission at λ ~ 1540 nm, but the lifetime increases with decreasing x. We have demonstrated the occurrence of energy migration and calculated the corresponding activation energy for the x = 0.3 and x = 1 samples. Using high pressure techniques, we also show that lifetime is reduced when reducing the Er-Er distance due to the enhancement of non-radiative de-excitation processes related to cross-relaxation. We also observe a pressure-induced phase transition at P ~ 2 GPa and a temperature-induced phase transition at T ~ 125 K. The general behaviour of the series is explained in terms of the occurrence of distance-dependent excitation transfer (excitation hopping and cross-relaxation). Findings for the Er series are compared with Yb[(p-CF₃-C₆F₄)₂PO₂]₃, in which only excitation migration takes place.

This work reports a correlation study between the crystal structure and photoluminescence (PL) in A₂MnX₄ (A: [CH₃]₄N; X: Cl, Br) by means of simultaneously optical spectroscopy and x-ray diffraction (XRD) under pressure. These materials are attractive systems for PL studies under pressure since they are very compressible and the interaction between organic/inorganic ((CH₃)₄N⁻/MnX₄²⁻) tetrahedra strongly affects the PL efficiency, which is fully related to the isolated T_d MnX₄²⁻. We show that pressure induces strong redshifts of emission peak of MnX₄²⁻ as well as decomposition processes at higher pressures yielding new aggregated phases of Mn²⁺ and amorphization which deeply affect Mn²⁺ PL. The equation of state of each compound is reported from XRD data.

The organic-inorganic hybrid quantum well compound, (C₁₀H₇C₂H₄NH₃)₂PbCl₄, exhibits enhanced phosphorescence due to the energy transfer from the excitonic state of inorganic quantum well to the triplet state of naphthalene chromophore. In the present study, photoluminescence and optical absorption spectra of (C₁₀H₇C₂H₄NH₃)₂PbCl₄ were investigated under pressure to 6.5 GPa in order to investigate the pressure dependence of the energy transfer. The phosphorescence intensity decreases with pressure up to 5 GPa, while the energy of the triplet state of naphthalene chromophore does not change with pressure. From the absorption spectra under pressure, it is found that the exciton energy of inorganic quantum well decreases with pressure up to 5 GPa. In our experiment, the energy transfer from the singlet state of naphthalene chromophore exited by ultraviolet light at 3.82 eV to the singlet exciton of inorganic quantum well occurs, and then the singlet exciton is converted to the triplet exciton by intersystem crossing, which is followed by the energy transfer to the triplet state of naphthalene chromophore for phosphorescence. Our observations on phosphorescence can be explained by a change in the energy difference between the excitonic state of inorganic quantum well and the singlet state of naphthalene chromophore with pressure.

In this work, the Raman scattering of melamine was studied under high pressure up to 25 GPa. Behavior of the most intensive peaks of the Raman spectrum of melamine, 677 cm⁻¹ and 985 cm⁻¹ modes, and their line widths do not show any phase transition or indication of formation of sp³ bonds. Comparing behavior of the line width of the Raman peaks of graphite under pressure and that of melamine leads us to conclude that the s-triasine ring is more rigid than the C-C graphite ring.

We have pressurized meso-carbon micro-beads (MCMBs) in combination with H₂ at room temperature and obtained the Raman spectra under pressure up to 2 GPa. The peak frequencies of G-, H-H stretching and H₂ rotational bands show simultaneous changes in the following pressure ranges: P ≤ 0.66 GPa, 0.66 GPa < P ≤ 1.0 GPa, and 1 GPa < P. Both the G-and H-H stretching bands show mode-hardenings in the pressure range up to 0.66 GPa. In the range between 0.66 and 1 GPa, the G-band shows the softening in addition to the invariable peak-frequency shift of H-H stretching band. At the pressures above 1 GPa, the both peak frequencies monotonously increase with increasing the pressure. According to previous x-ray diffraction observation, the a-axis length shows abrupt increase at 0.66 GPa. Taking the overlapping of wave functions between σ-bond of H₂ and π-bond of graphite into account, we speculate the followings: the intercalation of H₂ into the regulated nano-space of MCMBs at the pressures below 0.66 GPa, eliminating of H₂ from the nano-space in the range between 0.66 and 1 GPa, and hydrostatic compression of MCMBs by the eliminated H₂ at pressures above 1 GPa.

Raman and visible absorption spectra of AlH₃ were measured at high pressures in order to clarify the structural and electronic phase transitions. For the Raman results, abrupt decrease in Raman intensity was found at 30 GPa, implying that there exists a structural transition from the α phase to higher pressure phase. Correspondingly, the spectral change in the optical absorption was observed at almost the same pressure of 30 GPa. From the absorption measurements, the band gap is expected to close at the pressure higher than 50 GPa.

The electronic absorption and Raman spectra of CuWO₄ are studied as a function of pressure in the 0 – 20 GPa range. The below-gap absorption bands at 1.15, 1.38 and 1.56 eV correspond to Cu²⁺ d-transitions split by the Jahn-Teller distortion of CuO₆ (R_eq = 1.98 Å; R_ax = 2.39 Å; Q_θ = 0.47 Å). Pressure induces a strong reduction of the JT distortion up to 10 GPa. Above this pressure we observe, by optical absorption and Raman spectroscopy, a first-order phase transition at 11 GPa with phase coexistence in the 10–12 GPa range, as it is confirmed by Raman spectroscopy. The absorption spectra suggest that two different Cu²⁺ sites are formed in the high pressure phase, each having rather different CuO₆ distortion. The more JT distorted CuO₆ centre is stable up to 20 GPa. Rather than JT reduction, pressure induces reorientations of the CuO₆ octahedra in the high-pressure phase.

Optical absorption spectra of trigonal selenium have been measured at pressure up to 5 GPa using a diamond anvil cell with two kinds of pressure-transmitting media, that is, a mixture of methanol, ethanol and water, and a potassium bromide, to confirm no effects of them. With increasing pressure, the absorption edge shifts to a lower energy and the pressure coefficients of the absorption edge at atmospheric pressure obtained by using both pressure-transmitting media agree with each other. At high pressure, as more clearly observed in the spectra obtained by using a potassium bromide, the edge shifts to a lower energy become moderate near 3 GPa, where an abrupt decrease in intramolecular covalent bond length was observed. This result must be related to the transition of the electronic band structure in trigonal selenium at approximately 3 GPa.

We have performed a high pressure synchrotron mid-infrared study 1,3,5,7-cyclooctatetraene up to ~22 GPa and at ambient temperature in a diamond anvil cell. We have confirmed our prior observations of phase transitions via Raman spectroscopy and x-ray diffraction near 3-4 GPa, and 7-10 GPa. We have also observed chemical reaction culminating in irreversible dimerization/polymerization of the material above 15 GPa.

Infrared spectroscopic studies of various rare-earth compounds (f electron systems) have been made under high pressure, in order to probe their interesting electronic structures induced by pressure. High pressures have been generated with the use of diamond anvil cells (DAC's). To precisely perform IR reflectivity measurements of single crystal samples mounted in a DAC, the synchrotron radiation at SPring-8 has been used as a highly bright IR source. In this manuscript, the basic concept of the high pressure IR experiment using synchrotron radiation is introduced, and an example of obtained data for YbS and their physical interpretation are briefly discussed.

Infrared absorption spectra of δ-AlOOH and its deuterated form (δ-AlOOD) were measured at high pressure using a diamond anvil cell under a quasi-hydrostatic pressure condition using helium as a pressure-transmitting medium. Two absorption bands at 1180 cm⁻¹and 1330 cm⁻¹ involving vibrations of hydrogen and oxygen atoms shifted to higher frequencies with increasing pressure up to 10 and 12 GPa for δ-AlOOH and δ-AlOOD, respectively. In contrast, at higher pressures the two bands did not shift so much. The pressure-response on the infrared spectra has a close relationship to the symmetrization of the hydrogen bonds and change in the compressibility which was observed from X-ray diffraction measurements.

We propose an improved algorithm for the determination of shear wave velocity in iron under high pressure within the frame of an earlier proposed laser ultrasonics technique [1]. The modification is based on the observation that the signal identified at short propagation distances as a TT wave (the wave that is excited as the shear (T) wave at the diamond/iron interface and is reflected by the iron/diamond interface as a T wave) splits into two signals, a TT wave and another wave, which may be associated with a head wave, beginning from some threshold distance. This finding allows us to improve the accuracy of shear wave velocity determination. Statistical errors of the sample thickness and of the longitudinal and shear velocities measurements were found to be less than 2%.

Here we present a study of the elastic moduli of polycrystalline fullerites C₆₀ and C₇₀ in the temperature range 77–340 K at pressures up to 2.5 GPa using an improved ultrasonic technique. The comparison of the isothermal (quasistatic) and adiabatic (ultrasonic) bulk moduli has been realized for these fullerites. We have also shown the considerable difference in elasticity under pressure for fullerites C₆₀ and C₇₀.

The bulk physical properties of composite systems are difficult to predict – even when the properties of the constituent materials in the system are well known. We conducted a finite-element method simulation to examine the inclusion effect by substituting an inclusion phase (second phase) into a host phase (first phase). We have organized the simulation results as a function of the elasticity of host and inclusion phases. In this procedure, special attention was paid to the initial change of elastic constants as the inclusion volume ratio was varied. To accomplish this, we introduced a new parameter D_ij defined as the derivatives of the normalized stiffness elastic constant over the inclusion volume ratio. We succeeded in obtaining useful systematic formulations for D_ij. These formulations are expected to be applicable to the study of composite systems in many disciplines, such as geophysics, mechanics, material engineering, and biology. The present results provide much more effective constraints on the physical properties of composite systems, like rocks, than traditional methods, such as the Voigt-Reuss bounds.

Raman scattering experiments were carried out at pressure up to 296 GPa at low temperature. The behaviors of spectral data were consistent with previous results. The frequency of the vibron, however, did not show linear pressure dependence, contrary to the previous report. Darkening of the hydrogen sample was observed above 270 GPa. The band gap closure of solid hydrogen is expected to be 400 – 450 GPa. Diffraction data of phase III were obtained with monitoring the transition into phase III by in situ measurement of Raman vibron frequencies of hydrogen.

The challenge of confining hydrogen and its isotopes at high pressures and temperatures have hindered exploration of the predicted novel phases and their properties in static high P-T experiments. We have developed new methods to achieve good local confinement of hot, dense hydrogen that additionally protects the diamond anvils during the experiments. Raman spectra of such locally confined hydrogen and deuterium samples at high P-T conditions reveal interesting and rich features which include some that may be related to melting and some related to possible formation of species like metal hydrides and clathrates. These are discussed in the context of difficulties associated with establishing unambiguous diagnostics of melting of hydrogen, and thereby determination of the melting curve in laser and resistive heating diamond cell experiments at high pressures.

High-pressure Raman scattering measurements for the high-pressure phase III of methane hydrate (MH-III, filled ice structure) have been performed at pressures up to 25 GPa and at 296 K. We have observed the O-H stretching Raman signal in the MH-III phase by growing the MH-III crystals over several days at 1.9 GPa. The O-H stretching vibrational peak in the MH-III phase shows negative pressure dependence indicative of hydrogen bond and disappears above 14 GPa. The symmetrization pressure of hydrogen bond in the MH-III phase is estimated to be about 45 GPa from the pressure dependence of the O-H stretching Raman frequency, which is consistent with the previous theoretical prediction.

Structural changes and preferential cage occupancies were examined for ethane hydrate and ethane-methane mixed gas hydrates with five compositions in a pressure range of 0.2 to 2.8 GPa at room temperature. X-ray diffractometry and Raman spectroscopy showed the following structural changes. The initial structure, structure I (sI), of ethane hydrate was retained up to 2.1 GPa without any structural change. For the mixed hydrates, sI was widely distributed throughout the region examined except for the methane-rich and lower pressure regions, where sII and sH appeared. Above 2.1 GPa ethane hydrate and all of the mixed hydrates decomposed into ice VI and ethane fluid or methane-ethane fluid, respectively. The Raman study revealed that occupation of the small cages by ethane molecules occurred above 0.1 GPa in ethane hydrate and continued up to decomposition at 2.1 GPa, although it was thought that ethane molecules were contained only in the large cage.

High-pressure experiments of hydrogen hydrate were performed using a diamond anvil cell under conditions of 0.1–44.2 GPa and at room temperature. Also, high pressure Raman studies of solid hydrogen were performed in the pressure range of 0.1–43.7 GPa. X-ray diffractometry (XRD) for hydrogen hydrate revealed that a known high-pressure structure, filled ice Ic structure, of hydrogen hydrate transformed to a new high-pressure structure at approximately 35–40 GPa. A comparison of the Raman spectroscopy of a vibron for hydrogen molecules between hydrogen hydrate and solid hydrogen revealed that the extraction of hydrogen molecules from hydrogen hydrate occurred above 20 GPa. Also, the Raman spectra of a roton revealed that the rotation of hydrogen molecules in hydrogen hydrate was suppressed at around 20 GPa and that the rotation recovered under higher pressure. These results indicated that remarkable intermolecular interactions in hydrogen hydrate between neighboring hydrogen molecules and between guest hydrogen molecules and host water molecules might occur. These intermolecular interactions could produce the stability of hydrogen hydrate.

The storage capacity of H₂ in the THF, THT, and furan hydrates was studied by p-V-T measurements. We confirmed that the storage and release processes of H₂ in all hydrates could be performed reversibly by pressure swing without destroying of hydrate cages. H₂ absorption in both THT and furan hydrates is much faster than THF hydrate in spite of same unit-cell structure. On the other hand, the storage amounts of H₂ are coincident in the all additive hydrates and would reach at about 1.0 mass% asymptotically.

We have incorporated the translational- rotational (TR) coupling effects in the framework of three body force shell model (TSM) to develop an extended TSM (ETSM). This ETSM has been applied to reveal the second order elastic constants (C₁₁, C₁₂ and C₄₄) in the dilute regimes 0<x<1 in the temperature range 60K≤T≤300K.The anomalous elastic behaviour observed in C₄₄ in Brillouin scattering measurements for the composition x=0.20, 0.30 and 0.59 has been predicted well by ETSM results in the orientationally disordered (NaCN)_x(NaCl)_1−x mixed crystals. Besides, the results on cohesive and thermal properties are also discussed.

¹³C nuclear magnetic resonance (NMR) measurements under the application of hydrostatic pressure were carried out on the one-dimensional organic conductor, (TMTTF)₂SbF₆, to investigate the competed antiferromagnetic and spin-singlet ground states. The charge-ordering (CO) transition temperature, T_CO, (155 K at ambient pressure), decreased to 100 K under a pressure of 5 kbar, and was suppressed above 8 kbar. Under pressures between 5 kbar and 14 kbar, the low-pressure side antiferromagnetic state (AF-I) was suppressed. At the same time, a spin-gap phase was stabilized. Above 17 kbar, another antiferromagnetic phase appeared below approximately 15 ~ 20 K. A possible reentrant antiferromagnetic phase diagram is discussed from a microscopic point-of-view.

With the interest of ground state near CDW at low temperature, the electronic properties under high pressure, at low temperature and in high magnetic field of HMTSF-TCNQ are examined. Up to 8 GPa, the overall resistivity-temperature behaviour are unchanged, i.e. broad resistance minimum around 100–150 K and subtle resistance decrease below around 30 K. The pressure insensitive nature is not consistent with previous data. At 1.5–1.6 GPa, but not at P = 0, a novel hysteretic behaviour and probable quantum oscillations in magnetoresistance are found in a clear form.

By use of synchrotron radiation, powder x-ray diffraction of one-dimensional bis(dimethylglyoximato)Pd(II), Pd(dmg)₂ has been studied at high pressures. The lattice constants with an orthorhombic structure for Pd(dmg)₂ decreased with increasing pressure up to 10 GPa. The rate of the decrease of the b-axis was lower than that of the a-axis above 3 GPa. The c-axis is very compressible. A Pd-Pd distance along the c-axis abruptly decreased from 3.255 °A at ambient pressure to 2.82 °A at 7.4 GPa. A bulk modulus was estimated from the volume vs. pressure curve fitted by a Birch equation of state. The bulk modulus and its derivative of Pd(dmg)₂ were 9.9(7) GPa and 9.2(8). This complex is a very compressible compound. The electronic absorption spectra of a thin film of Pd(dmg)₂ have been investigated at high pressures. The 4d–5p transition bands rapidly shifted to lower energy region with increasing pressure. This optical transition energy decreased linearly with decreasing Pd-Pd distance. The optical property of Pd(dmg)₂ shows the one-dimensional character in the 0–6 GPa region.

We demonstrate a new apparatus for optical observation under high pressure conditions with 4-way optical glasses. We use the proposed apparatus to study solubility of ammonium salts in aqueous solutions and to measure the nucleation pressure for different concentrations of salts in the solution. Despite the fact that the solubility of electrolytes usually increases as the pressure increases, it is found that the solubility of ammonium salts decreases as the pressure increases. In both cases, high pressure can be used towards a crystallization process. Finally, we observe high pressure induced nucleation of electrolytes in an aqueous solution.

The solvation properties of some room-temperature ionic liquids consisting of imidazolium cations and various anions were examined by means of the high-pressure spectroscopy with solvatochromic probes. We measured the pressure dependence of Kamlet-Taft solvatochromic parameters (π*, β) and microviscosity (η). It was found that π* and β were not so sensitive to the types of imidazolium cations and polyatomic anions, but the type of monoatomic anions. The pressure dependence of microviscosity was found to obey the empirical power-law equation.

In situ Raman spectroscopic analysis has been performed for room temperature ionic liquid (RTIL) + CO₂ systems under two-phase equilibrium conditions at room temperature. The Raman spectra indicate the followings: the vibration state and configuration of 1-ethyl-3-methylimidazolium tetrafluoroborate change by CO₂ dissolution; the liquid structure of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide barely changes by addition of CO₂ pressure up to 30 MPa. In addition, the information of the RTIL structure suggests that the large change of the vibration state and configuration of the RTIL does not necessarily relate to the high CO₂ solubility in the RTIL.

We have measured Raman spectral changes of N,N,diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF₄]−H₂O mixtures under high pressure. All the Raman spectra of mixtures of water concentrations below 50.0 mol% H₂O changed at around 1 GPa at room temperature. The spectrum at high pressure is completely different from that obtained by cooling the sample at a normal pressure.

We have carried out Raman spectroscopic measurements on the anhydrous LnCl₃ • 20MeOH solutions (Ln³⁺=Pr³⁺ and Ho³⁺) as a function of pressure at room temperature. Pressure dependence of the frequency of the Ln-Cl Raman band (v_Ln-Cl) is examined in conjunction with the formation of chloro-complexes. We have found that the v_Ln-Cl wavenumber decreases with increasing pressure, which means that the higher chloro-complexes become dominant species at high pressures.

We have carried out Raman spectroscopic measurements on aqueous EuCl₃ • 20H₂O solution as a function of pressure at room temperature. Pressure dependence of the frequency shift of the totally symmetric stretching vibration of the aquo-europium earth ion (v_w) is examined in conjunction with the hydration number change. We found that the population of Eu³⁺ ion holding eight water molecules in their inner most hydration spheres increases with applied pressure, which means that the lower aquo-complexes become dominant species at high pressures.

Pressure-induced coordination structural changes of the acetate-rare earth complex in water (LnCl₃·20H₂O·CH₃COOLi) have been investigated using Raman spectroscopy. From the analysis of Raman CC stretching band of acetate ion, the integrated Raman intensity of polymeric chain structure decreases with increasing pressure throughout the rare-earth series. The monodentate ligand appears at around 0.6 GPa in the meddle-heavy rare earth region. We have determined the difference in the partial molar volume (PMV) (ΔV) among three coordination structures. The rank ordering of the PMV of three coordination structures is as follows: monodentate ligand <bidentate ligand <polymeric chain structure. The absolute values ΔV^{Polymeric→ Bidentate} and ΔV^{Bidentate→Monodentate} become larger with decreasing ionic radius of Ln³⁺ ion, and theses are probably due to the size effect of Ln³⁺ ion.

The movement of particles with a size smaller than few microns is governed by random Brownian motion. This motion causes the fluid to flow around the particles. The force acting upon Brownian particles as well as their velocities are measured by using the dynamic light scattering (DLS) technique. It provides the relationship between fluid shear stress and shear rate over the Brownian particle and determines the viscosity properties of the fluid. In this study, we propose a new rheometer which is widely applicable to fluid viscosity measurements at both normal and high pressure levels for Newtonian and non- Newtonian fluids.

Densities and Viscosities of N, N-dimethylformamide (DMF)-water (D₂O, H₂O) mixtures were measured at 5, 25, and 45°C under high pressure up to 196.1 MPa. The isothermal compressibility of the mixtures shows a minimum against the composition in the water-rich region and the depth of the minimum is larger at lower pressures and temperatures. The viscosity of the mixture exhibits a remarkable maximum in the water-rich region, and its maximum becomes larger with an increase in pressure and with a decrease in temperature. These results are discussed in terms of the interactions between DMF and water molecules, especially, the hydrophobic hydration around the methyl groups of DMF molecules.

In this paper, a method to analyze the temperature and pressure dependences of the viscosity or of the structural relaxation time in supercooled liquids is shown from the point of view of chemical bonding. The model used in this analysis is the Bond Strength–Coordination Number Fluctuation (BSCNF) model originally proposed by one of the authors. A theoretical relationship between the Vogel temperature T₀ of the well-known Vogel-Flucher-Tammann (VFT) equation and our model parameters which contain some microscopic information on bonding connectivity among the structural units that form the melt has been obtained. Using the theoretical relationship, we analyzed the dynamics of two kinds of molecular glass forming liquids under pressure, (a) 4,4'-methylenebis(N,N-diglycidylaniline), and (b) BMPC: 1,1'-di(p-methoxyphenyl)cyclohexane. The result obtained suggests that by applying pressure in these materials, the intermolecular cooperativity is suppressed due to increases in the mean total bond strength and the fluctuations of the structural units.

X-ray diffraction has been measured up to 2.4 GPa for liquid Ge_0.15Te_0.85 alloy using synchrotron radiations. Static structure factor S(Q) and pair distribution function g(r) were obtained. At 0.5 GPa, S(Q) shows different temperature dependence below and above 700 K. With increasing temperature above 700 K the increasing rate of the height ratio between the first and second peaks in S(Q) becomes moderated. This finding suggests a temperature-induced structural transformation occurs at 700K. At 1.8 GPa and 2.4 GPa such anomalous behaviour was not observed in the temperature region from the melting temperature to 850 K. The boundary between the low-temperature and the high-temperature phases has a negative slope. The Clausius-Clapeyron equation suggests the high-temperature phase has larger entropy than the low-temperature one.

We have done energy-dispersive x-ray diffraction for liquid As, Sb, GeS, GeSe, GeTe, and found that there is a relationship between medium-range order (MRO) and the Peierls distortion (or charge-density-wave structure) in these liquids. The prepeak disappears when the Peierls distortion is suppressed. In this paper we explain the relationship between MRO and Peierls distortion in liquids by a tentative assumption that the prepeak could be a remnant of satellite peaks in the Peierls-distorted crystals.

We have carried out small-angle x-ray scattering and x-ray transmission measurements of liquid Se₅₀−Te₅₀ mixture at SPring-8 in Japan and obtained the structure factor S(Q) at small-Q region (0.6 < Q < 3.5 nm⁻¹) and the density at high temperatures and high pressures up to 1000 °C and 180 MPa. We report preliminary results in this paper.

With increasing temperature, the density shows a minimum at around 500 °C and a maximum at around 700 °C. On the other hand, S(0) becomes maximum and S(Q) strongly depends on Q at around 600 °C, which is about the middle temperature where the density shows the minimum and maximum. The temperatures shift to lower side when the pressure increases. These results prove that, with increasing temperature, the sample exhibits gradual transition from low-density structure to high-density structure, which causes mesoscopic density fluctuations in the intermediate temperature region.

Structure of the liquid forms of tin tetraiodide, SnI₄, has been studied at high pressure and high temperature by synchrotron x-ray diffraction experiment. Using a new sample container, we managed to collect diffraction data with much better quality than before. The presence of two different liquid forms was verified. The structural change between these two liquid forms is expected to take place in a very narrow pressure range between 1.35 GPa at 850K and 2.03 GPa at 1000K.

In-situ x-ray diffraction measurement on liquid iron hydrogen alloy (FeH_x) was performed at 4 GPa and 1350°C. X-ray diffraction of pure liquid Fe was also measured at 3.5 GPa and 1700°C for comparison. The obtained structure factors for liquid FeH_x and pure Fe are very similar though the second peak in the structure factor for liquid FeH_x is more asymmetric. It suggests that hydrogen affects some local order in the liquid state. Slight elongation of the Fe-Fe nearest neighbour distance due to hydrogenation supports a notion that hydrogen and iron form interstitial alloy in the liquid state.

The homogeneous formation of liquid carbon without the partial melting of carbon specimen is very important to evaluate the physical properties of liquid carbon. The pyrolytic graphite was melted by the direct joule heating with current passed through the specimen along the direction parallel to c-plane. The resistivity of the liquid carbon at the melting point decreases from 630 to 470μΩcm with increase of pressure of 1.4 to 4.0GPa and then increases 490 to 565μΩcm with increase of 5.6 to 9.4GPa. The magnitude of resistivity of the liquid carbon at the melting point within this experiment indicates that the liquid carbon is a "poorly conductive metal". On the other hand the resistivity of liquid carbon tends to change from metal like behaviour (the temperature coefficient of resistivity dρ/dT> 0) to non-metal (or semiconductor) like one (dρ/dT<0) at the pressure of around 4GPa-5.6GPa. These results are considered to fortify our previous conclusion about the existence of the structural transformation of carbon in the liquid state [1].

The ac-conductivity of amorphous Ge-Au alloy has been measured at frequencies of 20 Hz to 1 MHz, at pressures up to 5 GPa and temperatures down to 77 K using a Drickamer-type high pressure cell. The ac-conductivity increases with increasing frequency. With increasing temperature, the rising frequency increases. From these results, temperature dependence of conductivity was obtained without shape parameters of the sample. The temperature dependence of hopping conductivity is found to be well described by a power law expected from the Multiphonon Process model. The exponent n in the power law increases with increasing pressure below 2 GPa, and decreases above 2 GPa. This pressure dependence of n agrees with the previous reported results from dc electrical resistivity measurements. The anomalous pressure dependence of n is discussed in relation to the Debye frequency, atomic distance, void size, and the density of states at the Fermi level.

By studying the pressure dependence of the fragility, it is expected that new horizons will open to understand the relaxation behaviour of supercooled liquids. However, as far as the authors are informed, no study has been performed on pressure dependence of the fragility in bulk metallic glass forming systems. In the present study, such dependence is investigated based on materials properties correlations. It is suggested that the effect of pressure on the fragility of bulk metallic glasses is very small. Our analysis indicates also that the fragility of metallic glasses will increase with the application of pressure. This behaviour contrasts with the behaviour observed in molecular systems, where the fragility remains almost constant or decreases slightly with the application of pressure. The result found is discussed in terms of the bond strength-coordination number fluctuation model of the viscosity.

Structure change of ground soda-silicate glass (SiO₂-Na₂O binary systems) was investigated using X-ray diffraction (XRD) and infrared spectroscopy. The measurement results were discussed comparison to that of SiO₂ glass. With increasing Na₂O concentrations, the XRD intensity around 2θ = 22° decreased and the intensity around 32° increased. The intensity around 22° and 32° maybe attributed to SiO₂ glass structure unit and soda-silicate glass unit, respectively. The peaks of Na₂CO₃ crystal for 2SiO₂-Na₂O glass were observed with increasing milling time. This crystallization was suggested that Na⁺ ion on 2SiO₂-Na₂O glass surface connected CO₂ in air. The intensity around 22° and 32° decreased and the intensity around 30° increased with increasing milling time. These may indicate that SiO₂ glass structure unit and soda-silicate glass structure unit were mixed by milling. In addition, IR absorption band near v = 1100 cm⁻¹ was separated to two bands near 940 cm⁻¹ and 1070 cm⁻¹ with increasing Na₂O concentrations. The band near 940 cm⁻¹ decreased and the band near 1070 cm⁻¹ increased with increasing milling time. These spectra changes were suggested due to decrease of Na₂O concentrations in 2SiO₂-Na₂O glass with Na₂CO₃ crystallization.

The density and structure of MgSiO₃ glass (v-En) recovered from a series of annealing experiments up to 1000°C at 2.0, 5.5 and 8.5 GPa have been investigated using Archimedes' method and Raman spectroscopy, respectively. The densities of recovered glasses are found to be a complex function of pressure and temperature. At room temperature, compression up to 8.5 GPa, followed by decompression, yields a glass with a density within 0.6 % of the 1-atm value. Likewise, the 1-atm density is fully recovered in glass heated up to ~500°C at 2.0 GPa at higher pressures. A sharp increase in recovered density is observed between 500°C and 800°C at 2.0 GPa, 200°C and 500°C at 5.5 GPa and from room-T and 300°C at 8.5 GPa. At higher annealing temperatures the changes in density are more modest. This break in slope occurs for a glass density of 2.89 g/cm³ at 2.0 GPa and 2.95 g/cm³ at 5.5 and 8.5 GPa. Above ~900°C v-En crystallizes at all pressures. Raman spectra for annealed glasses show a progressive shift in the Si-O-Si bending mode to higher wave number with recovered density. From these data we estimate a ~4.5 % decrease in the Si-O-Si bond angle with densification from 2.75 g/cm³ (1-atm, room T) to 3.0 g/cm³.

The phase equilibria of carbon dioxide (CO₂) + poly(methyl methacrylate) (PMMA; Mw = 15 k) + ethanol ternary systems were measured at temperatures ranging from 293.3 to 359.7 K and pressures up to 14.1 MPa. In order to determine the phase boundary, we observed the cloud points and bubble points by using a variable volume view cell. Furthermore, the dissolution process of PMMA in CO₂-expanded ethanol was studied using FTIR spectroscopy. Although both CO₂ and ethanol are nonsolvents for PMMA at 303 K, PMMA dissolved in CO₂-expanded ethanol. The noticeable band was carbonyl stretching band for PMMA. No peak shifts and/or no contributions were obtained for PMMA in pure ethanol at 303 K, because ethanol is nonsolvent for PMMA. With addition of CO₂ in the mixture of PMMA and ethanol, the carbonyl stretching band of PMMA has a weak contribution at lower wave numbers. It is indicated that a strong interaction between PMMA and ethanol via hydrogen bonding exists.

Polycaprolactone (PCL) is a Food and Drug Administration (FDA) approved biodegradable polyester used in tissue engineering applications. Ibuprofen is an anti-inflammatory drug which has good solubility in supercritical CO₂ (SCCO₂). The solubility of CO₂ in PCL allows for the impregnation of CO₂-soluble therapeutic agents into the polymer via a supercritical fluid (SCF) process. Polymers impregnated with bio-active compounds are highly desired for medical implants and controlled drug delivery. In this study, the use of CO₂ to impregnate PCL with ibuprofen was investigated. The effect of operating conditions on the impregnation of ibuprofen into PCL was investigated over two pressure and two temperature levels, 150bar and 200bar, 35°C and 40 °C, respectively. Polycaprolactone with drug-loadings as high as 27% w/w were obtained. Impregnated samples exhibited controlled drug release profiles over several days.

Supercritical fluid with plasma is a type of green processing media because this technique does not use catalyst and toxic solvents. In this study, we carried out experiments of organic materials in the presence of discharged plasma in sub- and supercritical water to evaluate the possibility for new reactions. For this purpose, we used SUS316 reactor that generates plasma at temperature and pressure up to 573K and 30MPa, respectively. 100 mmol/L aqueous phenol solution was used as starting material. The reactions were carried out at temperature of 523K and under pressure of 25MPa. After a series of reactions, water-soluble, water-insoluble (oily products), solid residue and gaseous product were obtained. For the analysis of these products, HPLC, GC-MS, TOC, GC-TCD and TOF-MS were used. The highest phenol conversion was 16.96% obtained at 523K, 25MPa and with 4000 times discharged plasma. Polymerized phenol was obtained as a product.

The time resolved fluorescence spectra of perylene in sub- and supercritical methanol have been measured by using a streak camera in the lower-pressure region than 10 MPa and an optical Kerr gate spectroscopic method in the higher-pressure region than 10 MPa. The lineshape of the fluorescence spectrum has been found to be dependent on the time. By comparing the excess energy dependence of the fluorescence lineshape in vapour perylene without energy dissipation process, the spectral change was assigned to the vibrational energy relaxation process in the S₁ state. The vibrational energy relaxation time at each solvent density in supercritical region was determined by the time-profile at the 0-0 band peak position in the fluorescence spectrum. The vibrational energy relaxation rate scaled by the square root of the temperature has been compared with the hydrogen-bonding degree between solvent molecules estimated by the NMR measurement (Hoffmann M M and Conradi M S 1998 J. Phys. Chem. B102 263).

Wide angle X-ray scattering measurements of sub- and supercritical water have been carried out using synchrotron radiation at SPring-8 in Japan, to study density dependence of the local structure. X-ray diffraction spectra were measured from 300 K to 1023 K at 40 MPa, and up to 1100 K at 100 MPa, corresponding to the density ρ from 1 g cm⁻³ to 0.10 g cm⁻³. The nearest neighbour distance and the nearest neibour coordination number depending on the density indcate that water is uniformly expanded from 1 g cm⁻³ to 0.6 g cm⁻³ with destruction of hydrogen bonding. With further volume expansion, the coordination number becomes approximately one at 0.15 g cm⁻³ while the nearest neighbour distance is approximately 3.3 Å. This experimental fact may be a first direct observation of dimeric molecules in the supercritical water.

The hybrid process of the hydrothermal gasification method and the TiO₂ photocatalysis has been developed and tested for the gasification of glucose. TiO₂ powder and those loaded with Pt or Ni were used as photocatalyst. 0.05 M glucose aqueous solutions suspending the photoctalysts were reacted by the flow-type reactor system in the dark or under near-UV illumination with pressure and temperature controlled to be 30 MPa and 350-450 °C, respectively. It was found that the evolutions of hydrogen and methane from glucose could be promoted by the photocatalytic action of TiO₂ under hydrothermal conditions, which was further enhanced by supporting Pt and Ni on TiO₂.

Femto-second transient absorption spectroscopy has been applied to investigate the back-electron transfer process after the photo-excitation of p-nitroaniline (PNA) in water from ambient to supercritical condition. After PNA was photo-excited at 400 nm, the bleach recovery signal was observed due to the back-electron transfer from the excited state to the ground state within about 1 ps. In the longer wavelength region above 400 nm, a transient absorption signal was observed due to the hot-band absorption which was produced from the back-electron transfer process to the ground state. The hot band decay rate was determined along the isochoric line from 298 K to 664 K at 40.1 MPa. The hot band decay rate increases from 298 K to 473 K, then it decreases to 664 K. The rate maximum was reproduced by the density and temperature dependence of the collision frequency, although the decrease at the higher temperature region was much more moderate for the hot band decay rate than is predicted by the collision frequency, suggesting the effects of the local density enhancement and the solute-solvent hydrogen-bonding.

The self-diffusion coefficients of water and organic solvents in the high-temperature high-pressure conditions are studied by using high-temperature NMR and MD simulation methods. The experimental results are analyzed using a scheme based on the solvation shell relaxation time obtained by MD simulation. The dynamic effect of hydrogen bonding is discussed through the comparison between water and a nonpolar organic solvent, benzene, over a wide range of density and temperature. The hydrogen-bonding effects are as follows: (1) the self-diffusion coefficient of water depends on density more weakly than that of benzene, (2) the self-diffusion coefficient of water at the ambient density depends on temperature more strongly than that of benzene at the density, (3) the turnover from the mobile-shell type to the in-shell type with increasing density does not occur in supercritical water up to the ambient density, whereas such turnover is observed in benzene. These contrasts are reflecting the dynamic effect of the anisotropic attractive interactions.

The Super-Critical Water-cooled Reactor (SCWR) has been designed and investigated because of its high thermal efficiency and plant simplification. There are some advantages including the use of a single phase coolant with high enthalpy but there are numerous potential problems, particularly with materials. As the operating temperature of supercritical water reactor will be between 280°C and 620°C with a pressure of 25MPa, the selection of materials is difficult and important. Austenitic stainless steels were selected for possible use in supercritical water systems because of their corrosion resistance and radiation resistance. The PNC1520 austenitic stainless steel developed by Japan Atomic Energy Agency (JAEA) as a nuclear fuel cladding material for a Na-cooled fast breeder reactor. The corrosion data of PNC1520 in supercritical water (SCW) is required but does not exist. The purpose of the present study is to research the corrosion properties for PNC1520 austenitic stainless steel in supercritical water. The supercritical water corrosion test was performed for the standard PNC1520 (1520S) and the Ti-additional type of PNC1520 (1520Ti) by using a supercritical water autoclave. Corrosion tests on the austenitic 1520S and 1520Ti steels in supercritical water were performed at 400, 500 and 600°C with exposures up to 1000h. The amount of weight gain, weight loss and weight of scale were evaluated after the corrosion test in supercritical water for both austenitic steels. After 1000h corrosion test performed, the weight gains of both austenitic stainless steels were less than 2 g/m² at 400°C and 500°C . But both weight gain and weight loss of 1520Ti were larger than those of 1520S at 600°C . By increasing the temperature to 600°C, the surface of 1520Ti was covered with magnetite formed in supercritical water and dissolution of the steel alloying elements has been observed. In view of corrosion, 1520S may have larger possibility than 1520Ti to adopt a supercritical water reactor core fuel cladding.

High-pressure phase transitions in CaRhO₃ were examined using a multianvil apparatus up to 27 GPa and 1930 ^oC. CaRhO₃ perovskite transforms to post-perovskite via a monoclinic intermediate phase with increasing pressure. Volume changes for the transitions of perovskite – intermediate phase and of intermediate phase – post-perovskite are -1.1 and -0.7 %, respectively. CaRhO₃ post-perovskite is the fourth quenchable post-perovskite oxide found so far. By high-temperature calorimetric experiments, enthalpy of the perovskite – post-perovskite transition in CaRuO₃ was measured as 15.2±3.3 kJ/mol. Combining the datum with those of CaIrO₃, it is shown that CaIrO₃ perovskite is energetically less stable than CaRuO₃ perovskite. This is consistent with the fact that orthorhombic distortion of CaIrO₃ perovskite is larger than CaRuO₃, as indicated with the tilt-angle of octahedral framework of perovskite structure. The transition pressure from perovskite to post-perovskite in CaBO₃ (B = Ru, Rh, Ir) increases almost linearly with decreasing the tilt-angle, suggesting that the perovskite – post-perovskite transition may result from instability of the perovskite structure with pressure.

Phase transformation from perovskite to "post-perovskite" and reserve transition in CaRuO₃ was observed by in situ X-ray diffraction at pressure of 20-22 GPa and temperature of 1173-1523 K. These pressure and temperature conditions are 1-2 GPa lower than previous results by quenched method. The axial compressibility is estimated to be a/a₀>b/b₀>c/c₀. This result is inconsistent with previous result on CaIrO₃.

Deformation microstructures of CaIrO₃ post perovskite (PPv) in a laser heated diamond anvil cell (DAC) are examined using transmission electron microscopy. Under a high stress and strain rate in the deformation condition, a high density of the {110} twin domains were at first time observed in post perovskite structure, as well as [100] and [001] dislocations on the (010) plane. The exchange of the a-axis for the b-axes in the twin mechanism can reduce a stress in a single crystal at the beginning of the uniaxial compression. The {110} plane in PPv corresponds with that of the crystallographic preferred orientation that was previously reported in deformed MgSiO₃ and MgGeO₃ PPv in DACs. This result implies that the formation of the twin domains can play an important role in CaIrO₃ PPv deformations under high stress and strain rate conditions (e.g., Deformation by DAC).

High-pressure high-temperature phase relation experiments in MgAl₂O₄ were performed in the pressure and temperature ranges of 18-27 GPa and 1400-2500 °C using a Kawai-type multi-anvil high-pressure apparatus. It was clarified that MgAl₂O₄ spinel directly transforms to the Mg₂Al₂O₅ + Al₂O₃ assemblage at about 20 GPa and temperature higher than 2100 °C. The experimental results indicates that the phase assemblage of Mg₂Al₂O₅ + Al₂O₃ is stable in the P-T region of 20 < P < 25 GPa and T > 2000 °C. The crystal structure of the Mg₂Al₂O₅ phase was refined by the Rietveld method using a structure model based on that of ludwigite. The calculated density of ρ_calc = 3.801(1) g/cm³ for the Mg₂Al₂O₅ phase is very consistent with the phase relations determined by the high-pressure high-temperature experiments.

High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes in conjunction with investigation of the spin transition in Fe²⁺ of (Mg_0.83Fe_0.17)O (ferropericlase, Fp). The Kawai-cell was squeezed in the DIA type press SPEED mkII installed at SPring-8. The volumes of the Fp and Au pressure standard were simultaneously determined by in situ X-ray diffraction using the synchrotron radiation. The maximum attainable pressure has reached 90 GPa at 300 K based on Anderson et al.'s Au scale [4]. The P-V data of (Mg_0.83Fe_0.17)O were acquired at 300 K and 700 K up to 90 GPa. From detailed analysis of the compression data, it is suggested that the spin transition proceeds over pressure ranges from 50 to 70 GPa at 300 K and from 50 to 75 GPa at 700 K.

There was a discrepancy between the seismic tomography and the elastic property of MgSiO₃ perovskite at near the D" zone and core boundary. Since a discovery of post-perovskite (ppv) of MgSiO₃, many investigations have made to explain the presence of low seismic velocity of the lower mantle and D" zone. However, precise experimental structure analysis of ppv-(Mg_1-xFe_x)SiO₃ has never been reported because of the experimental difficulty. Fe and Mg cation distribution and ordering in ppv-(Mg,Fe)SiO₃ in consideration of spins states are significant subject in lower mantle electronic and magnetic states. The present experiment aims X-ray emission study and structure analysis by Rietveld profile fitting of ppv-(Mg_0.6,Fe_0.4)SiO₃ by the precise powder diffraction measurement. Monte Carlo calculation proposed the reliable structures of iron-rich phase of ppv-(Mg,Fe)SiO₃: Pmmn, Pmma, and Cm2m and Cmcm proposed by. The best-fit structure model with the highest reliability in the Rietveld fitting of ppv-(Mg_0.6Fe_0.4)SiO₃ is the structure of space group Pmma, in which Fe and Mg occupy two different sites of M1 and M2: the site occupancies are (Fe_0.25Mg_0.75) in the larger M1 site and (Fe_0.55, Mg_0.45) in the smaller M2 site. The two-site model is consistence with the previous results of X-ray emission and X-ray Mössbauer experiments.

The phase boundaries between olivine, wadsleyite and ringwoodite have been studied comparatively under anhydrous and hydrous conditions with a fixed H₂O content of 1 wt% at 1673K. By comparing anhydrous and hydrous samples from the same experimental runs, we determined that two-phase coexisting loop in the olivine-wadsleyite boundary shifted towards lower pressure or lower iron content by the effect of H₂O, which is consistent with our previous work [1]. On the other hand, the loop in the wadsleyite-ringwoodite boundary shifted towards higher pressure or higher iron content, and the pressure width of the loop decreased. Thus, the presence of H₂O in the Earth's mantle will sharpen the 520-km seismic discontinuity, deep the depth of the discontinuity.

Electrical conductivity of mantle peridotite was measured at 25 GPa and temperature up to 1800 K in a Kawai-type multi-anvil apparatus. The starting material was gel with a composition of fertile spinel lherzolite (KLB1). After the conductivity measurement, mineral phases of run products are composed of magnesium silicate perovskite, ferro-periclase and Ca perovskite. The conductivity value of the peridotite is distinctly higher than those of post-spinel and magnesian silicate perovskite with a composition of (Mg_0.9,Fe_0.1)SiO₃, but lower than that of ferro-periclase. Both absolute values and change in activation enthalpy for the conductivity of the mantle peridotite are similar to those for the silicate perovskite. A presence of aluminous perovskite with substantial amount of ferric iron in crystal structure would enhance bulk conductivity of the lower mantle.

A theory of abiotic deep petroleum origin explains that hydrocarbon compounds are generated in the upper mantle and migrate through the deep faults into the Earth's crust. There they form oil and gas deposits in any kind of rock in any kind of the structural position. Until recently one of the main obstacles for further development of this theory has been the lack of reliable and reproducible experimental results confirming the possibility of the spontaneous synthesis of complex hydrocarbon systems at high pressure and temperature. Our experimental results demonstrate that abiotic synthesis of hydrocarbons under mantle conditions is a real chemical process. Different paths of hydrocarbon synthesis under mantle conditions are discussed. Obtained experimental results place the theory of the abiotic deep petroleum origin in the mainstream of modern experimental physics and physical chemistry.

High-pressure and high-temperature experiments of the olivine-methane-water system were performed using a laser-heated diamond anvil cell at pressure range from 5.8 GPa to 29.4 GPa and temperatures up to 2000K. The samples were examined by X-ray diffractometry and Raman spectroscopy under high pressures and room temperature. The heated areas of the samples changed to black color. Raman spectroscopy revealed the existence of ethane, heavier hydrocarbons, graphite and glassy carbon besides methane molecules. X-ray diffractometry showed that olivine was remained in the sample heated at 5. 8 GPa, 2000K. Wadsleyite and ringwoodite were observed in the samples heated at 14.5 GPa and 19.5 GPa, respectively. At 29.4 GPa, the diffraction line of Mg-perovskite and magnesiowustite were observed. The observed phase changes were similar to those observed in anhydrous and hydrous conditions. The present results suggest that polymerization of methane molecules occurred and that phase transition of olivine occurred even under the existence of methane-water fluid in the deeper part of the mantle.

We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P4₃2₁2 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm(00) [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 – 35.7 GPa) → Cmcm (35.7- 52GPa) → P4₃2₁2 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4/mcm(00) (134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm(00) above 495 GPa.

First principles total energy calculations as a function of unit cell volume have been performed on α (diamond structure), β (double bct), bct, bcc and hcp structures of tin. The comparison of total energies of these structures at various volumes suggests high pressure structural transitions of α → β → bet → bct at pressures of ~ 0.15 GPa, 2.7 GPa and 28 GPa. Also, 300 K isotherm upto maximum pressures of ~ 400 GPa has been determined for this metal. Using theoretical isotherm, shock Hugoniot of tin has been derived. Further, theoretically evaluated volume dependent Gruneisen parameter in conjunction with Lindeman melting law has been used to determine the pressure dependent melting of tin. The intersection of the theoretical melting curve with theoretically determined temperature rise with shock pressure reveals that this metal will melt at shock pressure of ~ 38 GPa (temperature ~ 1428 K) in good agreement with experimental value of 39 GPa (1550+100 K).

We have studied origins of the simple modulations of structures using first-principles calculations for group V, VI, and VII elements which have simple modulated structures. For the approximate structures which are defined by removing the modulations, we calculated phonon frequencies along the direction of the wave vectors of the modulation, and searched for possible phonon modes which may relate with the structural modulations. In phosphorus the Madelung energy works to destabilize the approximate monoclinic structure as well as the simple cubic and simple hexagonal structures, while it works to stabilize the approximate structures in other elements. Observing that the SC phase of phosphorus is stabilized by the band energies, we estimated the superconducting T_c in the SC phase. The calculated T_c remains at nearly same values in the SC phase. The electron phonon coupling increases with increasing pressure but the averaged phonon frequency decreases with increasing pressure, which is due to the increasing destabilizing effect of the Madelung energy.

In this work first-principle calculations on hcp and bcc Ti were performed using the wien2k package which is an implementation of the full-potential augmented-plane-wave method. It has been shown in our calculations that the electronic density of states at the Fermi level increases in the phase sequence α(hcp) → β(bcc) and this behavior is unambiguously reflected in all the theoretical data as well. Furthermore, the electronic density of state N(E_f), the energy of electrons for d and s-band and also the Fermi energy for both phases α and β were calculated. It was found that with an increase in pressure, the electrons of s-band will be transferred to d-band and the orbital of α- phase will be more localized than β- phase.

Barium silicide in the metastable trigonal phase is studied using ab initio methods. The band structure and the phonon spectrum are computed and analyzed. The electron-phonon coupling is found to have a substantial contribution coming from the A_1g optical mode at Γ. The superconducting transition temperature is calculated using the Allen-Dynes formula, but is found to be an order of magnitude smaller than the experimental value; some tentative explanations for the disagreement are presented.

An investigation into the structural stabilities of Fe₂P under high pressure is conducted using first-principles calculations based on density functional theory. Our results demonstrate that the stable phase of Fe₂P should be the Pnma with the lowest total energy at lower pressure, and the P2m and Pnma phases would transform to the Pmphase with larger coordination number of iron at 125 GPa and 153 GPa respectively. A magnetic moment collapse is observed at about 28 GPa in the P2m phase.

We calculated the electronic and lattice properties of 6H-AlN under various pressure conditions. The pressure conditions are hydrostatic, biaxial, and uniaxial compression and expansion. The 6H polytype has two structures. One is ABCBCB (ABC notation) and the other is ABCACB. 6H-AlN(ABCBCB) is energetically more favorable than 6H-AlN(ABCACB). Symmetry and hexagonality (H[%]) of 6H-AlN(ABCBCB) are P3m1 and 67 %, respectively. The electronic band structures of 6H-AlN polytypes under the ambient pressure show indirect band gaps. The band gap of 6H-AlN(ABCBCB) is closer to direct than that of 6H-AlN(ABCACB). The lattice properties of 6H-AlN(ABCBCB) under the various pressure conditions were optimized automatically by the first-principles molecular dynamics (FPMD) method. We also calculated the electronic band structures, the band gap values, the valence band maximum (VBM), and conduction band minimum (CBM) of 6H-AlN(ABCBCB) under the various pressure conditions. Their electronic band structures are non-metallic and band gaps are indirect with the exception of a few cases. The indirect band gap transforms to direct under expansion conditions.

A consistent calculation has been performed to describe the structural phase transition of NdAs using a well known three-body interaction potential model (TBIPA). Phase transition pressure is associated with a sudden collapse in the volume. The computed results on the phase transition pressure, volume collapse and pressure derivative of bulk modulus have shown a reasonably good agreement with their accurately measured data. In view of its overall success TBIPM has been regarded an adequate and appropriate model suitable for high-pressure studies.

In the present work we investigated theoretically the electronic, magnetic and structural properties of two rare-earth nitrides (REN: RE = Sm, Eu) by using self- consistent tight-binding linear muffin tin orbital (TBLMTO) method. Magnetically, both the rare earth nitrides (RENs) are stable in ferromagnetic (FM) state, while its ambient structure is found to be stable in NaCl-type (B₁) structure. From the present study we predict the pressure induced structural phase transition in both RENs from the relatively open NaCl-type structure into more dense CsCl-type structure at 8.6 GPa and 14.6 GPa respectively. They form a new class of half-metallic magnets with high magnetic moments and are strong candidates for applications in spintronics and spinfiltering devices. We have therefore, calculated electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli and magnetic moments for REN compounds in both B₁ and B₂ phases.

We have investigated theoretically the high-pressure structural phase transition and cohesive properties of two heavy rare earth mono antimonides (RESb; RE = Dy and Lu) by using two body interionic potential with necessary modifications to include the effect of Coulomb screening by the delocalized 4f electrons of the RE ion. The peculiar properties of these compounds have been interpreted in terms of the hybridization of f electrons with the conduction band and strong mixing of f states of RE ion with the p orbital of neighboring pnictogen ion. These compounds exhibit first order crystallographic phase transition from their NaCl (B₁) phase to CsCl (B₂) phase at 23.6 GPa and 25.4 GPa respectively. The bulk modulii of RESb compounds are obtained from the P-V curve fitted by the Birch equation of state. We also calculated the RE-RE distance as a function of pressure. Elastic properties of these compounds have also been studied and their second order elastic constants are calculated.

Full potential linear augmented plane wave (FP-LAPW) method is used to calculate the electronic structure of URh₃ in its AuCu₃ type structure as a function of reduced volume. The Fermi level lies near a maxima in the DOS and it remains pinned at the same position even at 40 GPa. The charge density plots show that the charge distribution becomes more uniform, the directional bonding decreases at very high pressure and the system becomes more metallic. The present analysis suggests that the AuCu₃ structure might remain as the ground state for URh₃ up to quite high pressures. A 2-D structural stability map constructed for the AB₃ type system indicates a wide structural stability regime for URh₃ under high pressure.

Recent discovery of a compound BC₅, whose structure is most likely diamond, invoked intensive interests in the superconductivity research. Little is known not only for its properties but for the preparation methods. For synthesizing BC₅, it is very important to know under what conditions this compound can be obtained. In this paper, density-functional-theoretic study has been made on the stability of BC₅ relative to a mixture of BC₃ and graphite as a function of pressure. It is shown that BC₅ becomes stable above 2 GPa. Therefore, high pressure synthesize is very useful.

Electronic structure of semiconducting boron carbide at high pressure has been theoretically investigated, because of interests in the positive pressure dependence of resistivity, in the gap closure, and in the phase transition. The most simplest form B₁₂(CCC) is assumed. Under assumptions of hydrostatic pressure and neglecting finite-temperature effects, boron carbide is quite stable at high pressure. The crystal of boron carbide is stable at least until a pressure higher than previous experiments showed. The gap closure occurs only after p=600 GPa on the assumption of the original crystal symmetry. In the low pressure regime, the pressure dependence of the energy gap almost diminishes, which is an exceptional case for semiconductors, which could be one of reasons for the positive pressure dependence of resistivity. A monotonous increase in the apex angle of rhombohedron suggests that the covalent bond continues to increase. The C chain inserted in the main diagonal of rhombohedral structure is the chief reason of this stability.

Quantum-mechanical molecular-dynamics simulations are carried out to explore possible precursor states of nano-polycrystalline diamond, a novel ultra-hard material produced directly from graphite. Large-scale simulation with 10⁵ atoms is realized by using the 'order-N' simulation code 'ELSES' (http://www.elses.jp). The simulation starts with a diamond structure that contains initial structural defects and results in a mixture of graphite(sp²)-like and diamond(sp³)-like regions as nano-meter-scale domains. We speculate that the domains are metastable and are possible candidates of the precursor structures.

Polymerization of C₆₀ molecular crystal under high pressure and high temperature is simulated by using linear scaling tight binding molecular dynamics (TBMD) with Graphic Processing Unit (GPU) as a computational accelerator for matrix-matrix multiplication. Two sets of tight binding parameters were tested.

Computational material design requires efficient algorithms and high-speed computers for calculating and predicting material properties. The orbital-free first principles calculation (OF-FPC) method, which is a tool for calculating and designing material properties, is an O(N) method and is suitable for large-scaled systems. The stagnation in the development of CPU devices with high mobility of electron carriers has driven the development of parallel computing and the production of CPU devices with finer spaced wiring. We, for the first time, propose another method to accelerate the computation using Graphics Processing Unit (GPU). The implementation of the Fast Fourier Transform (CUFFT) library that uses GPU, into our in-house OF-FPC code, reduces the computation time to half of that of the CPU.

We present a Graphics Processing Unit (GPU) accelerated simulations of first principles electronic structure calculations. The FFT, which is the most time-consuming part, is about 10 times accelerated. As the result, the total computation time of a first principles calculation is reduced to 15 percent of that of the CPU.

The crystal field splitting and d bandwidth of the 3d transition metal monoxides MnO, FeO, CoO and NiO are analyzed as a function of pressure within density functional theory. In all four cases the 3d bandwidth is significantly larger than the crystal field splitting over a wide range of compressions. The bandwidth actually increases more as pressure is increased than the crystal field splitting. Therefore the role of increasing bandwidth must be considered in any explanation of a possible spin collapse that these materials may exhibit under pressure.

The well-known Lennard-Jones potential is modified in such a way that it smoothly vanishes at a certain distance. A system whose interparticle interaction is given by such a potential is referred to as a modified Lennard-Jones system, and is served as a standard system describing simple solids and fluids. A phase diagram is determined based on the free energies obtained through thermodynamic integration.

A solvothermal process can be define as a chemical reaction in a close system involving different reactants in presence of a solvent (aqueous or non aqueous) at a temperature higher than its boiling temperature. Consequently pressure is involved. Two different cases are possible :(i) pressure is autogeneous and closely dependent of the percentage of filling for the reaction vessel and of temperature, (ii) pressure is imposed.

Solvothermal processes are governed by different key factors : (i) the composition of the reactants, (ii) the nature of the solvent (in particular its physico-chemical properties), (iii) the additives used and (iv) the thermodynamical parameters : temperature and pressure.

The main objective being to control the chemical mechanisms governing the preparation of the target material the selection of the key parameters is an important challenge for Solvothermal processes.

Solvothermal processes have been developed in different scientific fields as : (i) the synthesis of novel materials -in particular metastable materials with specific physical properties-, (ii) the crystal growth of functional materials for industrial applications, (iii) the preparation of nano-crystallites well defined in size and morphology and nano-composite systems, (iv) the deposition of thin nano-structured films...

During these last fifteen years, pressure was in the major cases an autogeneous pressure (pressure developed in the reaction vessel by only the thermal expansion of the liquid phase versus temperature).

An important challenge for the near future is to evaluate how pressure parameter can help the control of the reaction mechanisms governing the formation of the target product.

Production of lactic acid from C6-polyols (Mannitol) under alkaline hydrothermal conditions was investigated. Experiments were performed to examine the difference in the production of lactic acid between C6-polyols and C3-polyols (glycerine), as well as C6-aldoses (glucose). Results showed that the yield of lactic acid from C6-polyols was lower than that from both glycerine and glucose. It indicated that long chain polyols might follow a different reaction pathway from that of glycerine. Further investigation is needed to clarify the reaction mechanism and improve the relatively low lactic acid acid yield from C6-polyols.

The formation of formic acid or formate salts by hydrothermal oxidation of model biomass materials (glucose, starch and cellulose) was investigated. All experiments were conducted in a batch reactor, made of SUS 316 tubing, providing an internal volume of 5.7 cm³. A 30 wt% hydrogen peroxide aqueous solution was used as an oxidant. The experiments were carried out with temperature of 250°C, reaction time varying from 0.5 min to 5 min, H₂O₂ supply of 240%, and alkaline concentration varying from 0 to 1.25 M. Similar to glucose, in the cases of the oxidation of hydrothermal starch and cellulose, the addition of alkaline can also improve the yield of formic acid. And the yield were glucose>starch> cellulose in cases of with or without of alkaline addition.

Pristine aluminum was hydrogenated to form AlH₃ at 8.9 GPa and 600 °C. The cyclic formation and decomposition of the hydride were measured by in situ synchrotron X-ray diffraction measurement. AlH₃ synthesized under high pressure and temperature was recovered at ambient conditions. The recovered AlH₃ was characterized by conventional powder X-ray diffraction measurement and Raman spectroscopy. The results of the characterization were consistent with that obtained for chemically prepared AlH₃ and indicated that single phase α-AlH₃ was obtained.

High density nitrides and group IV alloys are of growing importance for both ceramic and optoelectronic applications. We present here new data and processes in our ongoing preparation of alkaline earth and transition metal nitrides as well as group IV alloys, here, up to 25 GPa and 2300 K. We employ large volume and laser-heated diamond anvil cell techniques for synthesis, processing tools including focused ion beam, and synchrotron X-ray diffraction, transmission electron microscopy and scanning electron microscopy for characterization.

Combined experimental and ab-initio computational studies suggest that at pressures above 20 GPa and temperatures above 1500 K sodium formate deprotonizes under formation of Na⁺₂ [C=O| CO₃^2-]. This new compound involves mesomeric C-O bonds with carbonate plus carbene units as limiting states and CO₂ chains as intermediate. Sodium is six-fold coordinated by O-atoms. The formation of this new compound implies nucleophilic addition as reaction mechanism which is consistent with previously observed reduced stability of the H-O bond at these high pressures. The findings suggest further that the sextet state of carbon is energetically less unfavourable at high pressure than at ambient pressure.

X-ray powder diffraction patterns of BaRu₄As₁₂ with synchrotron radiation have been studied at ambient pressure and at high pressures. A crystal structure of BaRu₄As₁₂ was refined by the Rietveld analysis of the x-ray powder diffraction data at ambient pressure. The electrical property of BaRu₄As₁₂ have been studied at low temperature. This arsenide shows the metallic behavior. The volume vs. pressure curve for this arsenide has in detail been investigated at room temperature. The cell volume of BaRu₄As₁₂ decreased smoothly with increasing pressure up to 10 GPa. A bulk modulus was estimated from the volume vs. pressure curve fitted by a Birch equation of state. The bulk modulus (B₀) and its pressure derivative (B₀') of BaRu₄As₁₂ are 127.0(2) GPa and 5.2(4), respectively. The value of B₀ for this arsenide is the same as that of CeRu₄As₁₂, smaller than that of LaRu₄As₁₂.

We found that two lithium niobate-type oxides, CdPbO₃ and PbNiO₃ were synthesized by high-pressure as metastable low-pressure perovskite-type phases. We then discussed the stability of lithium niobate-type and perovskite-type oxides relative to oxides with other structure for ABO₃ compounds. Consequently, the tolerance factor of perovskite is not the only predominant one to determine the stability and the crystal field effects of 3d transition metal ions are also important.

In this study, the effect of wide range of pressure (0.1~100 MPa) on low temperature synthesis of crystalline TiO₂ was investigated. Three different synthesis methods using acid catalyst, base catalyst and no catalyst were tried under three different pressure conditions such as atmospheric pressure, hydrothermal condition (about 0.27 MPa) and high pressure (10 ~100 MPa) at various temperature conditions (45 ~ 130 °C). The results showed that under atmospheric pressure, nanocrystalline anatase or rutile phase TiO₂ particles were obtained under the temperature below 100 °C for all the synthesis methods. Hydrothermal condition resulted in higher crystallinity anatase or rutile TiO₂ depending on the methods, however, slight reduction of specific surface area was observed. Applying higher pressure up to 100 MPa for the method using acid catalyst did not affect the resulting crystallite structure, however, slight decrease of crystallite size was observed with the increase of pressure.

Melting method for synthesizing BC_xN compounds has been improved, where the starting material is a mixture containing C and BN and wholly melted without reacting the container wall. Product is composed of two phases of BC_xN compounds. Their structures are cleared to be of the hBN-type and of the graphite-type, respectively. Variation of lattice parameters of the both phases and their formation ratio are investigated in relation to the composition of the starting mixture. Existence of ordered arrangement of B, C and N atoms is suggested, too. A structure model is given for the phase of the hBN-type.

Elastic properties of sintered diamonds with Co binder and binderless nano-polycrystalline diamond were determined by ultrasonic measurement at ambient condition. Elastic wave velocities of the sintered diamonds increase with increasing diamond content, and the nano-polycrystalline diamond, which was made by direct conversion of graphite and contains no binder, has the elastic wave velocities and elastic moduli significantly higher than those of the sintered diamonds with Co binder. The data suggest a great potential of the nano-polycrystalline diamond for industrial and scientific applications.

We synthesized a new phase from the B-C system, cubic BC₄ (c-BC₄), by direct transformation from graphitic phases at a pressure of 44 GPa and a temperature 2020 K in a laser-heated diamond anvil cell (DAC). Both x-ray diffraction and Raman spectroscopy confirm the presence of cubic BC₄ from the sample recovered at ambient conditions. The zero-pressure lattice parameter of the c-BC₄ calculated from diffraction peaks was found to be 3.587 Å. The composition of the new phase is determined from electron microprobe (EMP) measurements. The value of the C/B ratio is around 4 (3.91 ± 0.26).

Attempts have been made to synthesize nano-polycrystalline diamond (NPD) from graphite at pressures of 12, 13 and 14 GPa at temperatures 2200-2600°C using multi-anvil apparatus. The lower temperature limit for NPD formation increased with decreasing pressure, and we found that pure NPD can be synthesized even at the lowest pressure of 12 GPa, although quite high temperatures of exceeding 2600°C are required. This result demonstrates that NPD can be formed at significantly lower pressures than ever synthesized, which should provide an important constraint in synthesizing larger NPD samples under limited press loads.

Low-compressive new carbon-nitride-related materials were synthesized with a high-pressure and high-temperature treatment of CNHO nanoparticle prepared with an atmospheric nitrogen plasma. New phases were recovered at ambient conditions and the most prominent new phase is tentatively assigned to be an orthorhombic unit cell with the lattice parameters; a = 7.635 Å, b = 4.487 Å, and c = 4.040 Å.

Non-metallic and metallic solvents for growth of cubic BN at high pressure and high temperature were studied. When we used non-metallic MxByNz solvents such as Li₃BN₂, P-T region of cubic BN growth was separated into two regions namely rapid nucleation above 5 GPa and slow nucleation below about 5 GPa. In the slow nucleation region, cubic BN crystals were precipitated in the re-crystallized hBN matrix. When we use metallic solvents, (Fe,Co,Ni)-(Mo,Cr,V)-Al alloys, nucleation of cubic BN showed strong pressure dependent nature. It was found that B and N solubility can be controlled to select proper content of (Fe,Co,Ni)-(Mo,Cr,V) alloy system. Small amount of Al addition into the alloy system showed distinct increase the rate of nucleation of cubic BN.

High-pressure behaviour of Ta₃Si intermetallic compound was investigated by shock compression and static compression methods. Superconducting phase with T_C = 9.3 K was found in the sample shocked to 50-61 GPa, however most of the shock recovered sample indicated the starting stable phase with the Ti₃P-type structure. The new superconducting phase was not obtained from static compression up to 15 GPa and 800 °C. Bulk modulus of Ta₃Si with the Ti₃P-type structure was determined to be K₀ = 246(4) GPa. The present results suggest that a rapid phase transformation occurred during shock compression, but most of the high-pressure phase was reverted to the stable phase in the decompression process.

The elastic and thermal properties of perovskite manganites La_1−xSr_xMnO₃ (x = 0.165, 0.185, 0.20, 0.40, 0.70, 0.80, 0.90, 1.0) have been studied as a function of temperature (1K≤T≤300K) by means of Atoms in Molecules (AIM) theory and a Modified Rigid Ion Model (MRIM) respectively. The specific heat values (C_v) and the Debye temperatures obtained by us from the lattice contributions are in reasonably good agreement with the available experimental data for some concentrations (x) of La_1−xSr_xMnO₃. In addition, the results on the Bulk Modulus (B_T), cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (v_o) and Grüneisen parameter (γ) are also analysed.

Synthesizing processes of the binary antimony-based skutterudite compounds, CoSb₃, RhSb₃ and IrSb₃ at high pressures and high temperatures have been studied by means of in-situ x-ray diffraction measurements using synchrotron radiation and a cubic-anvil high-pressure apparatus. In series of the experiments, we could obtain the synthesis condition of these compounds under high pressure.

By use of synchrotron radiation, powder x-ray diffraction of the superconducting skuttetudites YT₄P₁₂ (T = Fe, Ru and Os) has been studied at high pressures. The d-values of many diffraction lines decreased monotonically with increasing pressure up to 10 GPa. New diffraction lines did not appear up to 10 GPa although the diffraction lines shifted and the width broadened with increasing pressure. The bulk moduli of these compounds were estimated from the volume vs. pressure curves fitted by a Birch equation of state. The bulk moduli of the superconducting skutterudites were 144 GPa for YFe₄P₁₂, 183 GPa for YRu₄P₁₂ and 189 GPa for YOs₄P₁₂. The bulk modulus of these skutterudites increased with increasing lattice constant. The similar results were also obtained for LaT₄P₁₂ (T = Fe, Ru and Os). The superconducting transition temperature (T_c) of YT₄P₁₂ (T = Fe, Ru and Os) is 7 K, 8.5 K and 3 K, respectively. YRu₄P₁₂ has the highest T_c among three skutterudites. The linear relation between T_c and bulk modulus is not found for the superconducting skutterudites YT₄P₁₂ (T = Fe, Ru and Os).

Many studies on superconductivity of boron-doped diamond (BDD) have been done, and it is well known that the superconducting transition temperature T_c of BDD films depend on the boron concentration and the growth direction. Uniaxial like pressure along (111) direction was applied on boron-doped (111) diamond films synthesized by CVD method using a diamond-anvil cell (DAC) up to 18.5 GPa. The T_c was decreased as previous report, however the changing rate is smaller than other experiments with hydrostatic pressures and a theoretical prediction.

Based on his 50-year career in static high-pressure research, P. W. Bridgman (PWB) is the father of modern high-pressure physics. What is not generally recognized is that Bridgman was also intimately connected with establishing shock compression as a scientific tool and he predicted major events in shock research that occurred up to 40 years after his death. In 1956 the first phase transition under shock compression was reported in Fe at 13 GPa (130 kbar). PWB said a phase transition could not occur in a ~microsec, thus setting off a controversy. The scientific legitimacy of shock compression resulted 5 years later when static high-pressure researchers confirmed with x-ray diffraction the existence of epsilon-Fe. Once PWB accepted the fact that shock waves generated with chemical explosives were a valid scientific tool, he immediately realized that substantially higher pressures would be achieved with nuclear explosives. He included his ideas for achieving higher pressures in articles published a few years after his death. L. V. Altshuler eventually read Bridgman's articles and pursued the idea of using nuclear explosives to generate super high pressures, which subsequently morphed today into giant lasers. PWB also anticipated combining static and shock methods, which today is done with pre-compression of a soft sample in a diamond anvil cell followed by laser-driven shock compression. One variation of that method is the reverberating-shock technique, in which the first shock pre-compresses a soft sample and subsequent reverberations isentropically compress the first-shocked state.

A series of shock-recovery experiments were performed on single crystals of silicon and germanium using a propellant gun and the laser-driven miniflyer method. Characterizations of the recovered samples by X-ray diffraction (XRD) analysis and Raman spectroscopy revealed the absence of additional constituents such as metastable phases and high-pressure phases. The XRD patterns for shocked samples are consistent with a powder XRD pattern corresponding to the cubic-diamond phase. The formation of copper silicide (Cu₃Si) was confirmed in the sample shocked at 38 GPa. The formation of an additional band and the deviation of a center frequency peak from the cubic-diamond phase of silicon and germanium were evident in the Raman spectroscopy results. The results of XRD and Raman spectroscopy indicated that crystalline size reduction, rather than the formation of metastable phases, occurred.

Here, we report a partially facetted carbon sphere of about 20 μm in diameter on the outer surface of the recovered sample from C₆₀ fullerene powder after shock-compression. The sphere has two hexagonal facets locating almost parallel to each other. Spotty contrast is observed on the roundish particle but not on the facetted area. Micro-Raman spectroscopy revealed that the facetted area is in a highly graphitized state but not the roundish area.

Structural change of synthetic opal by shock-wave compression up to 38.1 GPa has been investigated by using SEM, X-ray diffraction method (XRD), Infrared (IR) and Raman spectroscopies. Obtained information may indicate that the dehydration and polymerization of surface silanole due to high shock and residual temperature are very important factors in the structural evolution of synthetic opal by shock compression. Synthetic opal loses opalescence by 10.9 and 18.4 GPa of shock pressures. At 18.4 GPa, dehydration and polymerization of surface silanole and transformation of network structure may occur simultaneously. The 4-membered ring of TO₄ tetrahedrons in as synthetic opal may be relaxed to larger ring such as 6-membered ring by high residual temperature. Therefore, the residual temperature may be significantly high at even 18.4 GPa of shock compression. At 23.9 GPa, opal sample recovered the opalescence. Origin of this opalescence may be its layer structure by shock compression. Finally, sample fuse by very high residual temperature at 38.1 GPa and the structure closes to that of fused SiO₂ glass. However, internal silanole groups still remain even at 38.1 GPa.

Sapphire (single-crystal Al₂O₃) is an Earth material and a window in shock experiments. Pressure at the core-mantle boundary is ~130 GPa. Sapphire becomes opaque at 100-GPa shock pressures, which precludes measuring temperature with thermal radiance. Ruby is sapphire with a few 0.1% Cr. We have measured wave profiles of sapphire crystals with seven crystallographic orientations at shock pressures of 16, 23 and 86 GPa. At 23 GPa plastic-shock rise times are 1-300 ns, depend sensitively on the direction of shock propagation, and are totally contrary to conventional expectations. Long rise times are probably caused by strong inter-atomic interactions. Our wave profiles and published experiments and theory imply sapphire disorders without significant shock heating up to ~400 GPa, above which Al₂O₃ is amorphous and must heat. The characteristic shape of shock compression curves of many Earth materials at 100 GPa pressures is probably caused by a combination of entropy and temperature. Optimal shock windows are probably m- and s-cut crystals. Implications for the ruby scale, shock synthesis, and the ~$6B National Ignition Facility (NIF) are discussed.

Spall (dynamic fracture) strength of A12024-T4 and SS304 alloy have been determined at high strain rate. Gas gun experiments have been conducted on A12024-T4 and SS304 target plates in symmetric impact configuration. The spall in A12024-T4 and SS304 plates has been achieved by impacting them with parallel flying plates accelerated to velocities of 0.56 km/s and 0.6 km/s, respectively. The plate impacts in the two experiments introduced a shock wave of 4.38 GPa and 11.9 GPa, respectively in A12024 and SS304 target plates. In each experiment the interaction of tensile waves resulting from the reflection of shock wave from the target free surface and from the flyer free surface generated large tensile stress in the target which exceeded the spall strength causing spall fracture. The analysis of the velocity history of the target free surface recorded using VISAR reveals the dynamic yield strength of A12024-T4 to be 0.355 and spall strength of 1.46 GPa at strain rate of ~ 10⁴/s. These quantities in SS304 were determined to be 0.8 GPa and 2.69 GPa with strain rate of ~ 10⁴/s.

The Hugoniot response of materials is centrally important in the field of high pressure science. Highly accurate Hugoniot measurements not only provide better material references but also allow for the detection of subtle material phenomena. A process has been developed utilizing the Sandia Z accelerator to measure Hugoniot response at multi-megabar pressure resulting in extremely high accuracy data. Key considerations are the use of large surface area flyer plates allowing measurement configurations with multiple targets and diagnostics. This allows for greatly reduced uncertainty in the data. The details of this process are given and each aspect is closely examined focusing on the individual contributions to the overall accuracy of the result.

A laser-driven shock compression system using a table-top type pulsed laser was developed in order to investigate the Hugoniot equation-of-state (EOS) of laser-shocked materials. A line-imaging optically recording velocity interferometer system (ORVIS) was implemented for measurements of both shock wave velocity (Us) and particle velocity (up). The measurement of Hugoniot equation-of-state of nitromethane was performed by using the developed experimental system. The obtained experimental results showed a good agreement with the previous data. It was indicated that the developed experimental system and the analytical method implemented in this study were worked well and useful to investigate the Hugoniot equation-of-state of transparent materials such as nitromethane.

Coupling laser-shock and static-compression techniques allows to generate material conditions unreachable by either single-shock or static technique alone. Static compression experiments on water were performed using a precompression cell for laser-driven shock experiments. The pressure on static compression in this work was reproductively 1.3 – 2.3 times higher than in previous works and theoretical predictions. We have also performed static compression experiments using a new anvil material (Gd₃Ga₅O₁₂) to apply the cell to reflected shock compression. By coupling laser-driven reflected shock compression with precompression technique, it is possible to generate higher pressure and lower temperature range.

The conformational stability of [Leu]⁵-enkephalin,Tyr-Gly-Gly-Phe-Leu, in water have been investigated under high pressure by FTIR spectroscopy. Three peaks at 1638, 1650, and 1680 cm⁻¹ were determined by second derivative FTIR spectra in the amide I' region of [Leu]⁵-enkephalin. The peaks at 1637 and 1680 cm⁻¹ are assigned to the β-strand and turn structures, respectively. These peaks mean that [Leu]⁵-enkephalin takes a β-hairpin-like structure in water. Moreover, the absorbance at 1638 cm⁻¹ increases with increasing pressure, and this change shows a sigmoidal curve. Thus, we concluded that [Leu]⁵-enkephalin has the β-hairpin-like and disordered structures in water. From the FTIR profile at high pressures, the β-hairpin-like structure of [Leu]⁵-enkephalin is stabilized by a high pressures. Our result shows that the folded structures such as α-helix and β-hairpin structures of short peptide such as [Leu]⁵-enkephalin are stabilized at high pressures.

The effect of pressure on the α-helix structure of tetrameric coiled-coil peptides has been investigated using Fourier-transform infrared spectroscopy. To examine the influence of the hydrophobic core on pressure stability of the α-helices, the present study targeted GCN4-pLI and its variants (L9S, L9A, and L9G), which have different cavity in size. The amide II band was used to examine the stability of the hydrophobic core. From monitoring the amide I' band, it was shown commonly for all the peptides that the solvent-inaccessible α-helix decreases with increasing pressure while the solvent-accessible α-helix increases with increasing pressure. It was strongly suggested that the hydration of the helices is a significant factor for the pressure-induced folding. From further detailed analyses of pressure dependence of the amide I' band intensities, it was found that there is a positive correlation between the cavity size and the pressure-induced unfolding of the solvent inaccessible α-helix for the variants.

We have investigated the effect of pressure on the secondary structure of ribonuclease A using FTIR spectroscopy. In the presence of 47 %w/w sucrose, the intensity of an amide I' peak assigned to β-sheets of ribonuclease A was slightly recovered by applying pressure up to 200 MPa, while the peak was monotonically decreased with increasing pressure in the absence of sucrose. The present study is the first observation of the compression recovery of β-sheets in a protein by pressure in high concentration of sucrose. This result is consistent with a pressure perturbation calorimetric study (Ravindra et al. 2004 Phys. Chem. Chem. Phys.6 1952) reported that the sign of volume change of the protein thermal denaturation changed from negative to positive by adding sugars.

Pressure can retrain the heat-induced aggregation and dissociate the heat-induced aggregates. We observed the aggregation-preventing pressure effect and the aggregates-dissociating pressure effect to characterize the heat-induced aggregation of equine serum albumin (ESA) by FT-IR spectroscopy. The results suggest the α-helical structure collapses at the beginning of heat-induced aggregation through the swollen structure, and then the rearrangement of structure to the intermolecular β-sheet takes place through partially unfolded structure. We determined the activation volume for the heat-induced aggregation (ΔV^# = +93 ml/mol) and the partial molar volume difference between native state and heat-induced aggregates (ΔV=+32 ml/mol). This positive partial molar volume difference suggests that the heat-induced aggregates have larger internal voids than the native structure. Moreover, the positive volume change implies that the formation of the intermolecular β-sheet is unfavorable under high pressure.

Interactions of anti-fluorescent probe monoclonal antibody (immunoglobulin G (IgG)-49) with a ligand (fluorescein (FL)) and three kinds of inhibitors (1-tetradecanol (C14OH), 1-tetradecanoic acid (C13COOH) and 5-aminofluorescein (5-FLNH₂)) under high pressure were examined by methods of fluorescence spectroscopy. Pressure promoted the dissociation between FL and IgG-49 from the complex. The standard volume changes of the dissociation became negative, hence, the binding of FL to IgG-49 expands the volume of the complex. The volume expansion may be closely related to the large hydrophobicity around binding sites of FL in the IgG-49 molecule. Further, the standard volume changes of IgG-49 for the inhibitor binding, which were calculated from the Johnson-Eyring plots, became all negative. The volume change for 5-FLNH₂ was smaller than those for C14OH and C13COOH. This means that the volume of IgG-49 shrinks by the addition of the inhibitors in contrast with the FL binding. The differences among inhibitors are attributable to the differences in interaction modes to IgG-49 among them.

Three-dimensional nucleation rates J and induction times τ of glucose isomerase (GI) crystals were measured by counting the number of observable micro crystals with time in situ under high pressure. We also determined the solubility C_e under high pressure from the dependence of the growth and dissolution rates of the crystals on GI concentration C, and calculated supersaturation σ (σ ≡ ln(C / C_e)) under high pressure. Both J and τ⁻¹ increased with increasing pressure at the same σ. This indicates that the nucleation of the GI crystals was kinetically accelerated with pressure.

We successfully measured equilibrium temperatures T_e of tetragonal hen egg-white lysozyme crystals under high pressure by in situ observation of steps on the {110} faces of the crystals. The dependence of T_e on the concentration of lysozyme corresponds to that of the solubility C_e on temperature. The precision of the solubility determined in this study is significantly higher than that in previous works. One T_e could be measured during short time less than 70 minutes. This method for solubility measurements of protein crystals under high pressure is the fastest one at this stage.

We determined thermodynamic properties of phase transitions between bilayer and nonbilayer for phosphatidylcholines with saturated hydrophobic chains (C18:0-PC, O-C18:0-PC) and phosphatidylethanolamines with unsaturated ones (C18:1(cis)-PE, C18:1(trans)-PE) by means of calorimetry under ambient pressure and optical measurements under high pressure. The thermodynamic quantities of the transitions between bilayer and nonbilayer were much smaller than those of the transition between bilayers (gel-liquid crystal or hydrated crystal-liquid crystal transition) for the corresponding phospholipids. Although the nonbilayer formations correspond to a dynamic transformation between lamellar structure and nonlamellar structure, we can say that the order of the lipid molecule in both structures may not appreciably change judging from the smaller thermodynamic quantities. A notable feature of the bilayer-nonbilayer transitions is the large pressure dependence of the transition temperature as compared with that of the bilayer-bilayer transitions. Comparing the enthalpy and volume changes of the bilayer-nonbilayer transitions with those of the bilayer-bilayer transitions, we concluded that the former transitions can be regarded as the volume-driven transitions for the reconstruction of molecular packing.

The bilayer phase behavior of di-O-hexadecylphosphatidylethanolamine (DHPE), one of ether-linked phosphoethanolamines (PEs), was investigated under atmospheric and high pressure by means of differential scanning calorimetry (DSC) and high-pressure light-transmittance techniques. The gel-to-liquid-crystalline phase transition was observed at 67.1 °C under atmospheric pressure. The transition enthalpy was estimated to be 31.7 kJ mol⁻¹. Also under high pressure, only the same type of phase transition was observed, which means that DHPE cannot form the interdigitated structure even under high pressure. In general, it is known that the PE headgroup has an inhibitory effect against the interdigitation, whereas the presence of the ether linkage is advantageous to that. The result in this study indicates that the strong interaction by the formation of the hydrogen bonding network between the PE headgroups completely abolishes the capability of the phospholipid to form the interdigitated structure. By comparing the result with the previous results for the ether-linked phospho-choline (PC) and the ester-linked PC and PE lipids, we speculate on the mechanism of the transformation into the interdigitated structure induced by pressure in terms of the molecular interactions between the lipid molecules in the bilayer membrane.

The bilayer phase transitions of a series of mixed-chain phosphatidylcholines (PCs) with an unsaturated chain in the sn-1 position and saturated chain with different lengths in the sn-2 position, 1-oleoyl-2-myristoyl-PC (OMPC), 1-oleoyl-2-palmitoyl-PC (OPPC) and 1-oleoyl-2-stearoyl-PC (OSPC), were observed by differential scanning calorimetry (DSC) under ambient pressure and light transmittance measurements under high pressure. All the PC bilayer membranes exhibited not only the main transition from the lamellar gel (Lβ) phase to the liquid crystalline (Lα) phase but also the transition from the lamellar crystal (Lc) to the Lβ (or Lα) phase. The thermodynamic quantities of the transition between the Lc and Lα phases for bilayers of unsaturated mixed-chain PCs were compared with those of the corresponding mixed-chain PCs with saturated acyl chains such as 1-stearoyl-2-myristoyl-PC (SMPC), 1-stearoyl-2-palmitoyl-PC (SPPC) and 1,2-distearoyl-PC (DSPC). It turned out that the partial molar quantities of the unsaturated mixed-chain PC bilayers in the Lc phase are larger than those of the saturated mixed-chain PCs bilayers. The increase in the partial molar quantities in the Lc phase by the introduction of a cis double bond into the sn-1 acyl chain is attributable to the loose packing of the saturated and unsaturated acyl chains in the Lc phase.

Pressure perturbation calorimetry (PPC) is a relatively new technique based on a commercially available calorimeter which enables us to determine the isobaric coefficient of the thermal expansion of a solute for aqueous polymer solutions and colloidal dispersions. We applied the PPC to the investigation on the volume behaviour of dipalmitoylphosphatidylcholine (DPPC) bilayer membrane and compared the obtained results of the expansivity α₂ and the apparent molar volume ϕ₂ of DPPC in its bilayer membrane with those from a conventional densitometry. The temperature dependence of ϕ₂ from the PPC was in good agreement with that from the densitometry. Both techniques revealed that the α₂ value changes with the phase state of the DPPC bilayer membrane in the order of ripple gel (P_β') phase > liquid crystalline (L_α) phase > lamellar gel (L_β') phase. From the dependence, also the change of ϕ₂ at the main transition from the P_β' phase to the L_α phase was estimated to be 22.7 ± 2.62 cm³ mol⁻¹ from the PPC and at 24.0 cm³ mol-¹ from the densitometry, which are comparable with 25.4 cm³mol⁻¹ previously obtained by the calculation based on the Clapeyron equation. On the other hand, the change of ϕ₂ at the pretransition from the L_β' phase to the P_β' phase could not be determined with sufficient reliability. This may be due to the small change in ϕ₂ at the pretransition (less than 0.5% of ϕ₂ at the temperature).

It was shown by the present authors group that a tardigrade in its tun-state can survive after exposed to 7.5 GPa for 13 hours. We have extended this experiment to other tiny animals searching for lives under extreme conditions of high hydrostatic pressure. Artemia, a kind of planktons, in its dried egg-state have strong environmental tolerance. Dozens of Artemia eggs were sealed in a small Teflon capsule together with a liquid pressure medium, and exposed to the high hydrostatic pressure of 7.5 GPa. After the pressure was released, they were soaked in seawater to observe hatching rate. It was proved that 80-90% of the Artemia eggs were alive and hatched into Nauplii after exposed to the maximum pressure of 7.5 GPa for up to 48 hours. Comparing with Tardigrades, Artemia are four-times stronger against high pressure.

It was shown by the present authors group that tardigrade can survive under high pressure of 7.5 GPa. In the case of land plants, however, no result of such experiment has been reported. We have extended our experiments to moss searching for lives under very high pressure. Spore placentas of moss Venturiella were sealed in a small Teflon capsule together with a liquid pressure medium. The capsule was put in the center of a pyrophillite cube, and the maximum pressure of 7.5 GPa was applied using a two-stage cubic anvil press. The pressure was kept constant at the maximum pressure for12, 24, 72 and 144 hours. After the pressure was released, the spores were seeded on a ager medium, and incubated for one week and more longer at 25°C with white light of 2000 lux. It was proved that 70-90% of the spores were alive and germinated after exposed to the maximum pressure of 7.5 GPa for up to 72 hours. However, after exposed to 7.5 GPa for 6 days, only 4 individuals in a hundred were germinated. The pressure tolerance of moss Venturiella is found to be stronger than a small animal, tardigrade.

The effects of pressure on the survival rate of astrocytes in growth medium (DMEM) were investigated at room temperature and at 4°C, in an effort to establish the best conditions for the preservation. Survival rate at 4°C was found to be higher than that at room temperature. The survival rate of astrocytes preserved for 4 days at 4°C increased with increasing pressure up to 1.6 MPa, but decreased with increasing pressure above 1.6 MPa. At 10 MPa, all astrocytes died. The survival rate of cultured astrocytes decreased significantly following pressurization for 2 hours and the subsequent preservation for 2 days at atmospheric pressure. Therefore, it is necessary to maintain pressure when preserving astrocytes. These results indicate that the cells can be stored at 4°C under pressurization without freezing and without adding cryoprotective agents. Moreover, it may be possible to use this procedure as a new preservation method when cryopreservation is impractical.

We have previously reported that the survival rate of astrocytes increases under high-pressure conditions at 4°C. However, pressure vessels generally have numerous problems for use in cell preservation and transportation: (1) they cannot be readily separated from the pressurizing pump in the pressurized state; (2) they are typically heavy and expensive due the use of materials such as stainless steel; and (3) it is difficult to regulate pressurization rate with hand pumps. Therefore, we developed a transportable high-pressure system suitable for cell preservation under high-pressure conditions. This high-pressure vessel has the following characteristics: (1) it can be easily separated from the pressurizing pump due to the use of a cock-type stop valve; (2) it is small and compact, is made of PEEK and weighs less than 200 g; and (3) pressurization rate is regulated by an electric pump instead of a hand pump. Using this transportable high-pressure vessel for cell preservation, we found that astrocytes can survive for 4 days at 1.6 MPa and 4°C.

The inhibitory effect of compressed gaseous C2 compounds on yeast growth was investigated quantitatively by microcalorimetry. The growth thermograms (heat output vs. incubation time) showed that all C2 compounds tested inhibited yeast growth. After quantification of yeast growth at various pressures, we determined the 50% inhibitory pressure (IP₅₀) and the minimum inhibitory pressure (MIP) as indices which represent the inhibitory potency of gases. The lower the IP₅₀ and MIP values, the greater the growth inhibitory effects of the gases. Based on these values, the inhibitory potency of the gases increased in the order: ethane (C₂H₆) < ethylene (C₂H₄) < pentafluoroethane (C₂HF₅) < 1,1,1,2-tetrafluoroethane (C₂H₂F₄). Furthermore, transmission electron microscopy (TEM) of yeast cells treated with compressed ethylene showed that the inner structures of the cells, especially the nuclear membrane and cytoplasmic membrane, were damaged.

The kinetic process of pressure-induced gelation of whey protein isolate (WPI) solutions was studied using in situ light scattering. The relationship of the logarithm of scattered light intensity (I) versus time (t) was linear after the induced time and could be described by the Cahn-Hilliard linear theory. With increasing time, the scattered intensity deviated from the exponential relationship, and the time evolution of the scattered light intensity maximum I_m and the corresponding wavenumber q_m could be described in terms of the power-law relationship as I_m~f^β and q_m~f^−α, respectively. These results indicated that phase separation occurred during the gelation of WPI solutions under high pressure.

In this study, the effects of high-pressure treatment on structure and allergeincity of alpha amylase inhibitor (a-AI) were investigated. The pressure-induced structural changes of α-AI were estimated by fluorescence spectra and by fourth derivative UV-spectroscopy for probed tyrosine residues and by circular dichroism (CD) spectroscopy. The changes in the tertiary structure detected by fluorescence spectra and by fourth derivative UV-spectroscopy under high pressure were indicated at over 300 MPa. Measurements of CD spectroscopy suggested that the effects of a high-pressure treatment on changes in the secondary structure of α-AI were little. From our results, pressure-induced changes of the α-AI structure were not apparent. On the other hands, the IgE-specific binding activities of pressurized α-AI to sera from allergic patients against wheat, which is estimated by observations of dot-blotting, were decreased by high-pressure treatment. It is known that the pressure-induced elimination of allergenicity is related to the tertiary structural changes of allergen molecules. This study are suspected that the epitopes of α-AI do not contain tyrosine residues, and thus the decrease of IgE-specific binding activities is probably caused by the tertiary structural changes of these parts of α-AI.

High hydrostatic pressure (HP) with approximately below 400 MPa can induce a transformation of food materials to an alternative form, where membrane systems are damaged but certain enzymes are still active. HP treatment of water soaked brown rice grain could modify the mass transfer inside and apparent activities of enzymes, resulting in HP-dependent change of distribution of free amino acids. Thus, the distribution of free amino acids in brown rice grain during preservation after HP treatment was analyzed. Just after HP treatment at 200 MPa for 10 min, the distribution of free amino acids was not apparently different from that of untreated control. In contrast, after 1 to 4 days preservation at 25°C, amino acids, such as Ala, Glu, Gly, Asp and Val, showed higher concentrations than those in control. This result suggested that HP treatment induced proteolysis to produce free amino acids. However, Gln, Thr and Cys, showed no apparent difference, suggesting that conversion of certain amino acids produced by proteolysis occurred. Moreover, the concentration of γ-aminobutyric acid (GABA) in HP-treated sample was higher than that in untreated control. These results suggested that HP treatment induced alteration of distribution of free amino acids of rice grains via proteolysis and certain amino acids metabolism pathways.

Food treatments implying high pressures used pre-packaging systems; consequently it appeared necessary to validate different packaging films able to be used in such processes. Two different packaging films from AMCOR FLEXIBLES have been evaluated:

• VIROFLEXAL: BOLSA 80 MICRAS, coextrusion PA/PE (20/60μm)

• RILTHENE: SEMI 20/60 MICRAS, laminate PA/PE (20/60μm)

Three different physico-chemical characterizations have been developed for the evaluation of films behaviour after High Hydrostatic Pressure (HHP):

• (i) Mechanical properties (tensile strength and sealing strength),

• (ii) Oxygen permeability,

• (iii) Migration, through the contact with four food simulating liquids FSLs (water, acetic acid 3%, ethyl alcohol 10%, iso-octane).

Two different pressures values (P = 400MPa and 500MPa) have been tested, with a duration of 15 min, at ambient temperature (+20°C) and only one pressure (P = 200MPa) for the experiments at low temperature (T = -20°C) with the same duration (15min).

The selection of such values can be justified taking into account that experimental conditions as a temperature close to +20°C and a pressure between 400 and 500MPa are appropriated to inactivate bacteria and different others micro-organisms. Due to the efficiency of the association of hydrostatic pressure processing and low temperature (HHP/LT) [1, 2], the same films have been tested under high pressure processing (200MPa) but at negative temperature (−20°C).

A new high-pressure high-shear stress viscometer for pressure up to 400MPa, Couette type (rotational), has been developed. The wide shear rates range and shear stress can be applied for investigations of non-Newtonian liquids. The moment of viscous forces, acting in measuring viscosity cylinders, are measured outside of high-pressure chamber using primary method or using moment (force) sensors. That was realized by use of two counter rotating drive shaft systems with computer controlled stepped motors. As a pressure source a 10:1 intensifier with high-pressure manganin sensor were used.

A new controlled-clearance pressure balance is under development with the aim of improving the hydraulic high-pressure standard up to 1 GPa. This pressure balance consists of three parts: (i) a pressure generation device up to 1 GPa, (ii) a weight-loading unit which can load/unload weights automatically and independently, (iii) a controlled-clearance piston-cylinder which is designed to allow the jacket pressure to be applied independently. Some adjustments were made for loading heavy weights on/off the piston safely, keeping them in balance, then generating the pressure stably. Stability of the generated pressure was checked for several piston-cylinders, and it was found that pressure fluctuation was less than a few parts per million. The jacket pressure coefficient of a 500 MPa controlled-clearance piston-cylinder was precisely evaluated as a function of both the system pressure and the jacket pressure.

We describe a simple cryostat combined with a device for uniaxial compression up to 4 kbar that permits optical measurements and a moderate electroluminescence wave length tuning at liquid nitrogen temperatures.

The rheological properties of solidified oils including Daphne 7373 and 7474 under high pressure up to 5 GPa were evaluated by observing the large plastic deformation of metal microspheres due to nonhydrostatic pressurization in these oils using a diamond-anvil pressure cell. The solidification pressures determined by the onset pressures of deformation for aluminum microspheres are about 0.6 GPa for traction oils, 1.2 GPa for mineral oils, and 1.79 GPa for Daphne 7373 at 24 °C. Microsphere deformation for Daphne 7474 was not observed up to 3.51 GPa. Shear stresses of the solidified oils were estimated from the deformed Cu microspheres, treating them as stress sensors based on several assumptions.

Ruby fluorescence spectra were statistically compared in between a 4:1 methanol-ethanol and its deuterated mixture under high pressure in the DAC. It was confirmed that the isotope substitution in the pressure transmitting media results in no distinctive difference in the peak shape and pressure shift of the R1 and R2 lines in the ruby fluorescence spectra up to around 25 GPa. These results suggest that the pressure-induced solidification/glass transition between these hydrogenated and deuterated liquids has no isotopic effect within experimental uncertainties.

We evaluated the qualities of pressure-transmitting media by the ruby fluorescence method at room temperature, 77 and 4.2 K in the diamond anvil cell (DAC) up to 10 GPa in order to find appropriate media for the low temperature experiment. Investigations were done on fourteen kinds of media: a 1:1 mixture by volume of Fluorinert FC-70 and FC-77, Daphne 7373 and 7474, NaCl, silicon oil (polydimethylsiloxane), vaselin, 2-propanol, glycerin, a 1:1 mixture by volume of n-pentane and isopentane, a 4:1 mixture by volume of methanol and ethanol, petroleum ether, nitrogen, argon and helium. We discuss the non-hydrostatic effects of the pressure in the media from the broadening effect of the ruby R₁ fluorescence line. At the low temperature region, the non-hydrostatic effects develop continuously with increasing pressure from the low-pressure region in the all media. We reveal the relative strengths of the non-hydrostatic effects appeared in the media at 77K.

We fabricated a small Bridgeman anvil cell with a barrel-like shape for measurements under high-pressure up to 8 GPa. A Teflon cell with an inner volume of 1.5 mm in diameter and 2 mm in length is inserted in the pyrophyllite gaskets and is fixed between upper and lower tungsten-carbide (WC) anvils. The anvils are fastened by a Cu-Be holder with an outer diameter of 40 mm and 43 mm in length. Both of the top and bottom edges of the holder are tapered. This barrel-like shape enables rotation in a superconducting magnet with an inner diameter of 54 mm. The pressure is calibrated by measuring the resistivity of Bi at room temperature. The resistivity of Bi changed under loads at 8.0, 8.45, and 14.7 tons, corresponding to the structural phase transitions.

We report a technique for the precise measurement of the electrical resisivity under high pressure at low temperature by using Bridgman anvils made of tungsten carbide. Quasi-hydrostatic pressure is generated up to ~15 GPa in the relatively large working space which allows the use of large specimens and simple experimental procedures rather than using a standard diamond anvil cell. The application is demonstrated by the measurements of the electrical resistivity of lead in order to describe the effect of pressure on the superconducting transition.

We have successfully measured the Hall effect of a single crystal of a high temperature superconductor La_2−xSr_xCuO₄ in moissanite-anvil high pressure cells. A pressure cell with new Zylon-gasket and wiring arrangement survived under pressure up to at least 5 GPa. Pressure which was clamped at room temperature increased with lowering the temperature down to below 60 K by a factor of 1.3-1.4.

The second nonlinear susceptibility, χ⁽²⁾, reflects magnetic domain formation. At zero DC field, the temperature dependence of χ⁽²⁾ can be obtained through that of the third-harmonic AC susceptibility, χ_3ω. Generally, the magnitude of χ_3ω is at most a few percent of the linear component, χ_1ω, connected with the linear susceptibility, χ⁽⁰⁾. At GPa-level pressures generated using a diamond anvil cell, the detection of χ_3ω becomes more difficult, because of the small amount of measurement sample. We propose an effective method of measuring χ_3ω using a superconducting quantum interference device magnetometer and a statistics average technique. The experimental results for an inorganic chiral magnet, Cr_1/3NbS₂, indicate the efficiency of this technique and demonstrate that magnetic signals of the order of 10⁻⁹ emu can be detected.

The high pressure nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) are conventionally performed up to 3 GPa using piston cylinder cell. However, the NMR/NQR measurements beyond this pressure range are scarcely performed owing to the technical difficulty. Recently, we developed new high pressure NMR/NQR technique using cubic anvil apparatus in which highly hydrostatic pressure was obtained. Using the new method, the ⁶³Cu-NQR signal of Cu₂O was observed up to 7.2GPa with high sensitivity. The use of MgO gasket in mini-cubic anvil apparatus was examined for enlarging pressure range.

We have developed high-pressure, high-field and multi-frequency ESR apparatus. The pressure is available up to 14 kbar by using the clamped-type piston-cylinder pressure cell. All inner parts of the pressure cell are made of zirconia which has good transmittance of the electromagnetic wave in the frequency region from 70 to 700 GHz. The magnetic field region is up to 55 T and the temperature region is from 1.6 to 4.2 K. We present the results of quantum spin systems SrCu₂(BO₃)₂ and CsCuCl₃ as the application of this multi-extreme condition ESR technique and they will demonstrate its usefulness for studying the quantum spin system.

In this paper we present details of a technique of measurement of the thermoelectric power (Seebeck effect) at high pressure to 30 GPa. Two examples of its application are displayed as follows: lead (Pb) and bismuth telluride alloys (Bi₂Te₃ and In_xBi_2−xTe₃). For lead a kink in the pressure dependence of the thermopower near 13 GPa has been established and addressed to the structural fcc → hcp phase transition. The (In,Bi)₂Te₃ thermoelectrics exhibited a pressure-driven improvement of the thermoelectric parameters, such as thermoelectric power factor (efficiency) and the dimensionless figure of merit. The reasons of this enhancement are discussed.