Table of contents

Ba(Zr_xTi_1-x)O₃ (BZT) thin films with different Zr contents were deposited on (100) MgO and (100) Pt/(100) MgO substrates by RF-magnetron reactive sputtering using metal targets. The BZT (0 < x < 0.89) thin films had a single perovskite phase with only (001)/(100) orientation. In all cases, the ratio of Ba/Ti was stoichiometric according to X-ray fluorescence spectrometry (WDX) measurement. Atomic force microscopy (AFM) study proved that BZT films possess a dense microstructure without cracks or voids. The grain size was found to decrease with increasing of Zr content. The effect of Zr content on the dielectric constant and leakage current was studied. BZT thin films showed ferroelectric-to-paraelectric properties with increasing Zr content and excellent leakage properties according to measurements of electrical properties. These results indicated that we succeeded in depositing high-quality and low-sputter-damage BZT thin films by reactive sputtering using metal targets.

Cross sections of textured BaTiO₃-based thick films prepared by screen printing were successfully analyzed by electron backscatter diffraction and scanning electron microscopy. The textured thick films were prepared by repeating the screen printing and firing processes three times. During the firing of the third layer, the calcined powder formed round particles that were integrated into the grain. The results of crystal direction map analysis of the cross sections of the thick films showed that the degree of <100> orientation increased as the firing time increased. This tendency agrees with the change in the value of the Lotgering factor. Many 111 double twins were observed in the textured thick films, which may have facilitated the formation of the textured BaTiO₃ thick film.

Lead-free ferroelectric K_0.5Na_0.5NbO₃–CaZrO₃ thin films were prepared by chemical solution deposition. Chemically optimized K_0.5Na_0.5NbO₃–CaZrO₃ precursor thin films crystallized in the perovskite single phase on Pt/TiO_x/SiO₂/Si substrates at 650 °C. The K_0.5Na_0.5NbO₃–CaZrO₃ thin films showed poor ferroelectric polarizations due to the insufficient insulating resistance. The leakage current of the K_0.5Na_0.5NbO₃–CaZrO₃ films, especially in the high-applied-field region, was markedly reduced by 1 mol % Mn doping for the Nb site. Also, the ferroelectric properties of the K_0.5Na_0.5NbO₃–CaZrO₃ thin films depended on CaZrO₃ concentration. 1 mol % Mn-doped K_0.5Na_0.5NbO₃–CaZrO₃ thin films exhibited slim and small ferroelectric polarization–electric field (P–E) hysteresis loops at room temperature with an increase in CaZrO₃ amount. Furthermore, these films showed a typical field-induced displacement curve with a small hysteresis, and the estimated effective d₃₃ values were 32 pm/V for the 1 mol % Mn-doped 0.95K_0.5Na_0.5NbO₃–0.05CaZrO₃ thin films and 21 pm/V for the 1 mol % Mn-doped 0.9K_0.5Na_0.5NbO₃–0.1CaZrO₃ thin films.

The origin of the ferroelectricity of Bi(Mg_1/2Ti_1/2)O₃ films was investigated. Epitaxial Bi(Mg_1/2Ti_1/2)O₃ films with film thicknesses of 50 to 800 nm were grown on (111)_cSrRuO₃/(111)SrTiO₃ substrates by pulsed laser deposition. A Bi(Mg_1/2Ti_1/2)O₃ film was not strongly clamped from the substrate and identified to have rhombohedral symmetry with a = 0.398 nm and α= 89.8°, which was independent of film thickness within 100 to 800 nm. The relative dielectric constant, remanent polarization, and coercive field of the Bi(Mg_1/2Ti_1/2)O₃ films at room temperature were almost constant at about 250, 60 µC/cm², and 240 kV/cm, respectively, for film thicknesses above 200 nm. These data suggest that Bi(Mg_1/2Ti_1/2)O₃ films are ferroelectric.

Well-controlled polycrystalline (1-x-y)(K_0.5Na_0.5)Nb_0.95O₃–xBaTiO₃–yBaZrO₃ (KNN–BTO–BZO; 0≤x,y ≤0.1) thin films were systematically synthesized on Pt/TiO_x/SiO₂/Si substrates by the chemical solution deposition (CSD) method in order to improve the piezoelectric properties by the formation of the morphotropic phase boundary (MPB). The synthesized thin films exhibited excellent insulated resistance and ferroelectric properties. Experimental results indicated that the tetragonal structure was fabricated in the range of at least 0.05≤x ≤0.1 in (1-x)KNN–xBTO, whereas the rhombohedral structure was not formed at room temperature in the range of 0≤y ≤0.1 in (1-y)KNN–yBZO thin films. Therefore, the desired MPB between tetragonal and rhombohedral structures was not formed in the fabricated KNN–BTO–BZO thin films, which hinders the improvement in the piezoelectric property of d₃₃^* from that of (K_0.5Na_0.5)Nb_0.95O₃. This finding demonstrates that the original composition control with the consideration of the effects of the strain from substrate and the small grain size is indispensable for further improvement in the piezoelectric properties of KNN thin films.

0.92(Na_0.5K_0.5)NbO₃–0.06BaZrO₃–0.02(Bi_0.5Li_0.5)TiO₃ (NKN–BZ–BLT) thin films were fabricated by pulsed laser deposition (PLD) on a (100)Si substrate on which a 100-oriented LaNiO₃ (LNO) bottom layer was fabricated by the chemical solution deposition method. The NKN–BZ–BLT films were characterized by X-ray diffraction (XRD) analysis, θ/2θ scan and ψ–2θ/ω scan, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The properties were compared with those of the NKN–BZ–BLT film deposited on the (111)Pt/Ti/SiO₂/(100)Si substrate. We demonstrated that the LNO layer plays an important role in obtaining 100-oriented NKN–BZ–BLT films on the Si substrate. SEM surface and cross-sectional images showed that the NKN–BZ–BLT films fabricated at a substrate temperature of 800 °C had a high density and a relatively smooth surface. From the TEM image, this NKN–BZ–BLT film fabricated at 800 °C was composed of the columnar grains and some vertical-long pores could be observed. The energy dispersive X-ray (EDX) analysis showed that the LNO layer is decomposed to La₂NiO₄ by its reaction with Nb. The dielectric properties showed that the NKN–BZ–BLT film on the LNO electrode had a small dielectric constant of 82, compared with the NKN–BZ–BLT film (ε_r = 3127) on the (111)Pt/Ti/SiO₂/(100)Si substrate. This difference is due to the polarization direction of the film and the polarization axis of the NKN–BZ–BLT film on the LNO electrode exists in a direction perpendicular to the surface of the substrate. However, the NKN–BZ–BLT film on LNO showed a small P_r value. This is due to the dispersion of Ni from the LNO layer.

We report a size dependence of switchable polarization in PbTiO₃ nanoislands with heights of 2–7 nm and widths of 40–80 nm. An atomic force microscopy (AFM) system that was capable of probing a switching charge from a single PbTiO₃ nanoisland using a conductive AFM tip as a top electrode has been developed. Using the AFM system, the switching charge as small as 10 fC was detected within a tolerance of ±4 fC. The switchable polarization (ΔP) over 150 µC/cm² was observed for the nanoislands as small as 5 nm in height, and ΔP rapidly decreased with the height below 5 nm. Comparing the height or thickness dependence of ΔP and stable domain states between the nanoislands and ultrathin films, it was found that the polarization in the nanoislands can be switched by external fields more easily than that in the ultrathin films. The decrease in ΔP of the nanoislands with the height below 5 nm can be attributed to the intrinsic size effects.

(Bi,Pr)(Fe,Mn)O₃ (BPFM) thin films were deposited on the conductive B-doped diamond coated polycrystalline diamond substrates by chemical solution deposition method. BPFM thin films were crystallized with random orientation on the polycrystalline diamond. The BPFM/B-doped diamond layered film showed polarization vs electric field (P–E) hysteresis loops without any influences of leakage current at room temperature. The remnant polarization 2P_r and the coercive field 2E_c at the maximum electric field of 1000 kV/cm were 135 µC/cm² and 700 kV/cm, respectively. In the range of room temperature to 130 °C, the prepared film capacitor showed saturated-loop shape in the P–E curve without influences of leakage current.

We successfully fabricated ferroelectric gate thin film transistors (FGTs) using solution-processed (Bi,La)₄Ti₃O₁₂ (BLT)/Pb(Zr,Ti)O₃ (PZT) stacked films and an indium–tin oxide (ITO) film as ferroelectric gate insulators and an oxide channel, respectively. The typical n-type channel transistors were obtained with the counterclockwise hysteresis loop due to the ferroelectric property of the BLT/PZT stacked gate insulators. These FGTs exhibited good device performance characteristics, such as a high ON/OFF ratio of 10⁶, a large memory window of 1.7–3.1 V, and a large ON current of 0.5–2.5 mA. In order to investigate interface charge trapping for these devices, we applied the conductance method to MFS capacitors, i.e., Pt/ITO/BLT/PZT/Pt capacitors. As a result, the interface charge trap density (D_it) between the ITO and BLT/PZT stacked films was estimated to be in the range of 10^-11–10^-12 eV^-1 cm^-2. The small D_it value suggested that good interfaces were achieved.

The A-site composition dependence of cubic pyrochlore Bi–Zn–Nb–O (BZN) thin films of dielectric tunable properties was investigated. (111)-textured BZN films with a wide range of Bi/Nb ratios (0.62–1.26) were fabricated by metal organic chemical vapor deposition. Raman spectral analysis revealed that by changing the Bi/Nb ratio in BZN films, the Bi concentration of the A-site mainly varied. Dielectric constant and dielectric tunability were found to increase with increasing Bi ion occupancy of the A site. These experimental findings suggest that the Bi occupancy of A site is an important factor for designing Bi based pyrochlore dielectric tunable materials.

In this study, a finely patterned lead zirconate titanate (PZT) film is fabricated by a combination of inkjet printing (IJP), chemical solution deposition (CSD), and surface energy controlling technology. We used patterned multilayer lower electrodes, which easily enable high surface energy contrast on the lower electrode area and achieved high accuracy patterning in the inkjet deposition process. The PZT film, which can be used as an actuator, has 2 µm thickness after iterating the set of surface treatment, inkjet deposition, and baking. This film has a dielectric constant (ε_r) of 1700, loss tangent (tan δ) of 0.05, remanent polarization (P_r) of 10 µC/cm², and coercive field (E_c) of 23 kV/cm. Piezoelectric coefficient d₃₁ estimated from a displacement of the membrane was determined to be 77 pm/V. These results suggest that this method is a candidate for piezo microelectromechanical system (MEMS) fabrication.

We examined the composition and orientation dependences of the piezoelectric properties by combinatorial sputtering. PbTiO₃ and PbZrO₃ were simultaneously sputtered to prepare composition gradient Pb(Zr,Ti)O₃ (PZT) films on Pt/Ti/Si substrates, and an almost linear composition gradient was observed in a range of Zr/(Zr+Ti) ratios from 0.33 to 0.76. Dielectric and piezoelectric properties attained maximum at the Zr/Ti composition close to the morphotropic phase boundary (MPB), which is consistent with that of PZT ceramics. 100-oriented PZT films showed a higher dielectric constant than the PZT films with the other orientations, while the PZT films with 111 + 100 mixed orientation showed larger values of e_31f. These results suggest that the a-axis orientation is dominant in the 100-oriented PZT films. In this study, we demonstrated that the combinatorial sputtering method enables the precise evaluation of the composition dependence of piezoelectric and dielectric properties.

This paper shows the electrical properties of ferroelectric thin films with large compressive residual stress. In this study, the large compressive strain was applied to lead zirconate titanate (PZT) thin films by designing the bottom electrode structure on a Si wafer. The materials selected for the bottom electrode were lanthanum nickel oxide (LNO) and lanthanum strontium cobalt oxide [LSCO; (La_0.5Sr_0.5)CoO₃] from the viewpoint of thermal expansion coefficients. As a result, the PZT thin films with morphotropic phase boundary (MPB) composition received compressive residual stress up to approximately 0.8 GPa from the bottom electrode even on a Si wafer. The compressive residual stress concomitantly increased with increasing LSCO layer thickness. In addition, the remanent polarization of the PZT thin films increased with increasing compressive residual stress.

100-oriented epitaxial Pb(Zr_0.65Ti_0.35)O₃ films with various film thicknesses from 0.1 to 3 µm were grown on (100)_cSrRuO₃ ∥ (100)SrTiO₃ and (100)_cSrRuO₃ ∥ (100)LaNiO₃ ∥ (001)CaF₂ substrates. The out-of-plane/in-plane lattice parameter ratio of the films on the CaF₂ substrates was larger than that on the SrTiO₃ substrates up to 1.1 µm film thickness, while (90°-α) (α was defined as the internal tilt angle) was almost 0°. Results of analysis of Raman spectra and piezoresponse images suggest that the 1.1-µm-thick film grown on the (100)_cSrRuO₃ ∥ (100)LaNiO₃ ∥ (001)CaF₂ substrate had tetragonal symmetry with a polar-axis orientation. Moreover, the saturation polarization values of the films measured from P–E hysteresis loops correspond to the two P_s values estimated from the thermodynamic theory, assuming the change in the polar direction due to the symmetry change to tetragonal, and from the crystal distortion in tetragonal symmetry. This can be explained by the large compressive stress from the CaF₂ substrate having a large thermal expansion coefficient.

We fabricated Pb(Zr,Ti)O₃ (PZT) films with different orientations and grain textures by the sol–gel method. The fabricated films were tested using the high accelerated lifetime testing system. As a result, films with coarse grain texture exhibited longer lifetimes and a higher acceleration factor than those with fine-grained texture. The film orientation did not affect the mean time to failure of the film. This suggests that breaking phenomena are strongly dependent on the number of grain boundaries.

Thin films of silicate-doped CaBi₄Ti₄O₁₅ were fabricated to enhance the insulating property of one-axis-oriented CaBi₄Ti₄O₁₅ films under an applied electric field. The crystalline phase of CaBi₄Ti₄O₁₅, a type of bismuth layer-structured dielectric (BLSD) compound, was successfully grown on (100)LaNiO₃/(111)Pt/TiO₂/(100)Si with the preferential orientation of the (001) plane by the addition of bismuth silicate with a nominal composition of Bi₁₂SiO₂₀ up to 1.00%. The crystallographic orientation of the (001)BLSD plane normal to the substrate surface was degraded by excessive bismuth silicate addition above 1.50%. The breakdown electric field was increased by bismuth silicate addition up to 2.00% without the degraded relative dielectric permittivity (ε_r) of approximately 230. The bismuth silicate could precipitate between the grain boundaries in the CaBi₄Ti₄O₁₅ films without an interface reaction or a solid solution that enhances the insulating behavior of the BLSD films.

We report aerosol deposition (AD) method for preparation of bismuth layer-structured ferroelectric thick films with enhanced ferroelectric and insulating properties. Constitution phase, crystal structure, polarization and leakage current properties of SrBi₂Ta₂O₉ (SBTa) thick films with thickness of 2–4 µm were investigated. While obtained as-deposited SBTa films have slight c-axis grain orientation, the degree of orientation for the films annealed at higher than 1000 °C was the same as that for sintered bulks. Fracture cross-sectional scanning electron microscopy (SEM) images revealed that the as-deposited SBTa films on glass substrates had a fully dense microstructure. The low leakage current density (J) of less than 10^-7 A/cm² at 1 MV/cm was observed for SBTa films annealed at less than 900 °C, and the SBTa films annealed at 900 °C indicated a remanent polarization (P_r) of 5.7 µC/cm², which is larger than that of sintered bulks (P_r of 4.7 µC/cm²) fabricated by conventional solid-state reaction using the same starting raw powder used for the AD method.

In this research, we demonstrated that defect states in sol–gel-derived SrTa₂O₆ (STA) thin films can be detected by a thermal simulated current (TSC) technique. We also tentatively explained leakage current properties using these defect states. Similar defect states were found in STA thin films that were annealed at 700 and 800 °C by the TSC technique. Defects that caused the TSC peak at measurement temperatures of 130–150 °C showed higher trap densities in the 800 °C-annealed STA thin film. These defects were likely to be caused by diffused Ti, which mainly contributed to the larger leakage current in the 800 °C-annealed STA thin film. Oxygen-vacancy-related defect states were also clearly observed with the change in measurement atmosphere from air to vacuum.

Sputtering damage of SrRuO₃ (SRO) films prepared by RF magnetron sputtering under various growth pressures was investigated by Raman spectroscopy and X-ray photoemission spectroscopy (XPS). Phonon modes that were related to Ru and Sr ions changed and XPS spectra shifted with decreasing growth pressure. These results indicate that Sr ions switched place with Ru ions in SRO films when the SRO films had sputtering damage under low-growth-pressure sputtering condition as determined from Raman spectroscopy and XPS measurement. The antisite ion content increased with decreasing growth pressure. The resistivity of the SRO films also increased with increasing antisite ion content. The dynamics of sputtering damage revealed that the antisite Sr and Ru ions were formed in SRO films.

Ferroelectric BaTiO₃ and antiferromagnetic BaFeO₃ are deposited alternatively by a pulsed laser deposition method with the aim of fabricating room-temperature multiferroic materials. X-ray diffraction (XRD) analysis reveals that the superlattice structure is fabricated with a designed periodicity and thin film quality is improved by increasing BaFeO₃ layers. Ferroelectricity and ferromagnetic properties are examined by the double-wave method (DWM) of D–E hysteresis loops, an XRD dilatometry, and a superconducting quantum interference device magnetometer. Our superlattice thin film shows multiferroicity, i.e., the coexistence of ferroelectricity and ferromagnetism, at room temperature.

BiFeO₃ (BFO) thin films have been grown on vicinal SrTiO₃ (STO) (001) substrates by dual-ion-beam sputtering. The Bi/Fe composition ratio was optimized by adjusting the beam current ratio of a dual-ion beam. The domain structure was controlled using a vicinal STO substrate along <100> and <110>. From the results of X-ray diffraction analysis and piezoelectric force microscopy, it is found that BFO thin films grown on vicinal STO along <100> and <110> show stripe and single-domain structures, respectively. It is found that the reduction in the length of non-180° domain walls improves leakage current characteristics, resulting in an enhancement of ferroelectric D–E characteristics. The single-domain BFO thin film shows excellent D–E hysteresis loops at room temperature, with a double remanent polarization (2P_r) and a double coercive field (2E_c) of 140 µC/cm² and 340 kV/cm, respectively.

⁵⁷Fe-enriched BiFeO₃ (BFO) thin films were fabricated on Pt/Ti/SiO₂/Si substrates from a stoichiometric precursor solution by chemical solution deposition process. The Bi/Fe molar ratio of the BFO thin films was about 0.93. The crystallinity and surface morphology of the BFO thin films were improved by using a single-sintering technique. Mössbauer spectra of the BFO thin films were measured at room temperature, and the valence state of Fe ions was confirmed to be Fe³⁺ only. One of the BFO thin films fabricated by single-sintering at 550 °C showed a relatively saturated P–E hysteresis loop. The remanent polarization P_r and the coercive field E_c at 10 kHz were 59 µC/cm² and 327 kV/cm, respectively, at room temperature.

The effects of epitaxial strain on the crystal structure and piezoelectric properties of (100) BiFeO₃ thin films were investigated. The epitaxial strain of BiFeO₃ thin films grown by pulsed laser deposition was controlled by adjusting film thickness and growth temperature. From the results of X-ray diffraction reciprocal space mapping and in-plane piezoelectric force microscopy, it is found that the crystal structure of BiFeO₃ thin films is a rhombohedral structure with tetragonal distortion, and that the extent of tetragonal distortion increases with decreasing film thickness and growth temperature. From the voltage-strain curves of the films, electric field strain is dominated by the piezoelectric effect in the low-voltage region, while the electrostrictive effect appears in the high-voltage region. It was found that piezoelectric strain increases with increasing extent of tetragonal distortion, which suggests that the piezoelectric properties of BiFeO₃ thin films can be improved using a mixture of two types of structural distortion.

The dielectric response of reduced 1.0 mol %-Ni-doped KTaO₃ single crystals was studied to determine the mechanism of the high dielectric constant of 160000, with a low dielectric loss of less than 0.1. The dielectric constant depends on the sample thickness, sample color, and electrode material. The obtained results strongly support the existence of a Schottky barrier at the interface between the crystal and electrodes, and we deduce that a large number of free electrons are essential for inducing the extrinsic dielectric effect.

Using a spin-forming-extended method, which is one of the template grain growth methods, one-directional grain-orientation control was performed in (Sr,Ca)₂NaNb₅O₁₅ (SCNN) ceramics. Rod like templates were prepared by the one-step flux method using the mixed salts of KCl and NaCl. In order to obtain the SCNN templates with a high aspect ratio, the two-step flux method in which Sr_0.95Ca_0.05Nb₂O₆ powder is utilized as the precursor was also examined. From these templates, the rectangular samples with c-axis orientation in the thickness direction were fabricated. The textured samples with an orientation factor of 0.9 and a remnant polarization of 7.4 µC/cm² were obtained using the resulting templates from the two-step flux method.

Orderly assemblies of BaTiO₃ (BT) cube-shaped nanocrystals (nanocubes) and BT–SrTiO₃ (ST) mixture nanocubes were fabricated on Pt-coated Si substrates directly by capillary-force-assisted solution self-assembly and heat treatment. These dielectric nanocubes aligned face to face in quite a wide region of 10×50 µm² on the average with a height of 1 µm. The local microstructure of the nanocube assembly was observed by high-resolution transmission electron microscopy. It was revealed that the lattice strain at the interface of the neighboring nanocubes was locally induced. The piezoresponse of the BT–ST mixture nanocube assembly showed a nonlinear curve and a stepwise behavior at a high poling field, which differed from the ferroelectric BT and paraelectric ST assemblies investigated by scanning probe microscopy. The characteristic behavior might be attributed to the interfacial lattice strain in mixture assemblies.

We demonstrated the size effect on the dielectric properties of BaZr_xTi_1-xO₃ (x = 0.2 and 0.25) ceramics that showed relaxor behavior. Fine-grained BaZr_xTi_1-xO₃ ceramics with micrometer- and nanometer-sized grains were fabricated by the two-step sintering method and aerosol deposition (AD) method, respectively. From the dielectric measurement, the permittivity of the BaZr_xTi_1-xO₃ ceramics markedly decreased with decreasing grain size below 3 µm. The permittivity of the BaZr_xTi_1-xO₃ nanograined ceramics decreased with increasing Zr content and was much smaller than the permittivity of the BaTiO₃ nanograined ceramics. These results indicated that the BaZr_xTi_1-xO₃ ceramics were more susceptible to the grain size effect than the pure BaTiO₃ ceramics. The dielectric responses to temperature and frequency suggested that the volume fraction of polar nanoregions decreased and the relaxor characteristics increased with decreasing grain size in BaZr_xTi_1-xO₃ ceramics.

Barium titanate (BaTiO₃,BT)–potassium niobate (KNbO₃,KN) nanocomplex ceramics with various KN/BT molar ratios were prepared by a solvothermal method. From a transmission electron microscopy (TEM) observation, it was confirmed that the KN layer thickness on BT particles was controlled from 5 to 40 nm by controlling KN/BT molar ratios. Their dielectric constants were measured at room temperature and 1 MHz, and the maximum dielectric constant of 370 was measured for the BT–KN nanocomplex ceramics with a KN thickness of 22 nm. TEM observation revealed that at a KN thickness below 22 nm, the BT/KN heteroepitaxial interface was assigned as a strained interface, while at 40 nm, the interface was assigned as a relaxed one. These results suggested that the strained heteroepitaxial interface could be responsible for the enhanced dielectric properties.

The temperature dependence of the complex relative permittivity in a relaxor ferroelectric solid solution 24Pb(In_1/2Nb_1/2)O₃–46Pb(Mg_1/3Nb_2/3)O₃–30PbTiO₃ (PIN–PMN–PT) crystal poled and depoled was measured from room temperature to 200 °C at various frequencies. The poled sample exhibits transitions from the ferroelectric (FE) phase to the relaxor (RE) phase on heating, and after that, the depoled one exhibits those from the RE phase to the glassy freezing phase on cooling. An RE-type dielectric dispersion with a weak frequency (f) dependence was observed. Such a dielectric dispersion in the RE state was found to be based on tweed domain structures observed by polarization light microscopy (PLM) and piezoelectric force microscopy (PFM) due to the competition between the antiferroelectric (AFE) and FE coupling in the RE state. The temperature dependence of complex permittivity with resonance- and relaxor-type dielectric dispersions in the poled and depoled samples was characterized by hierarchical domain structures.

Percolative BaTiO₃/multiwalled carbon nanotube (MWNT) composite thick films were developed using an aerosol deposition (AD) process at room temperature. Well-dispersed mixed powders with various volume ratios were utilized as the starting powders for AD, and dense BaTiO₃/MWNT composite thick films were successfully fabricated with the starting mixed powders with 0.01 vol % MWNTs. The existence of MWNTs in the composite films was confirmed using Raman spectroscopy. The composite films show a high relative dielectric constant (657 at 1 kHz), which is approximately 7 times larger than that (91 at 1 kHz) of the BaTiO₃ films. In addition, the strong frequency dispersion of the dielectric constant in the low-frequency range was confirmed for the composite films. The dielectric properties of the composite films were investigated using the dielectric mechanism used in percolative composites.

We clarified the effect of (Ba,Ca)/Ti ratio on the substitution of Ba by Sn in (Ba,Ca)TiO₃ perovskites. With decreasing (Ba,Ca)/Ti ratio, c/a ratio rapidly increases and leads to an increase in phase transition temperature. The increasing number of Ba site vacancies is effective for substituting Sn into the Ba site. We directly observed that Sn ions exist at Ba sites, for the first time, by spherical-aberration-corrected scanning transmission electron microscopy combined with energy-dispersive X-ray spectrometry and electron energy loss spectroscopy. These results provide insights for exploring BaTiO₃-based ceramics containing Sn, which show high Curie temperatures without Pb.

The vanadium distribution in multilayer ceramic capacitors (MLCCs), sintered under a reducing atmosphere, was investigated using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS), and insulation resistance degradation was analyzed using impedance spectroscopy in highly accelerated lifetime tests to clarify the effects of vanadium on both the electrical properties and microstructure of MLCCs. Vanadium mitigated insulation resistance degradation and increased the reliability of MLCCs. Moreover, vanadium content increased and insulation resistance at the ceramic/electrode interface decreased slowly. This change in dynamics directly resulted in an improved lifetime of MLCCs. The results of STEM–EELS analysis showed that vanadium distributed along the grain boundary and grain boundary junction, but substituted into BaTiO₃ at the ceramic/electrode interface. Therefore, it is considered that vanadium substitution at the ceramic/electrode interface improves the reliability of MLCCs.

The environmental reliability of lead-free (K,Na)NbO₃-based multilayer ceramics with nickel inner electrodes was studied. The multilayer specimen with good piezoelectric properties was successfully obtained by adding excess zirconium to a (K,Na)NbO₃-based composition. Excess zirconium probably accelerated the solid solution of potassium into the crystal lattice and prevented potassium evaporation. The electric resistivity and piezoelectric properties of the ceramics were extremely stable at a high temperature (85 °C), a low temperature (-40 °C), and a high humidity [85 °C/85% relative humidity (RH)]. Their change rates were below 10% in 500 h studies. The stability was also high in the thermal shock (from -40 to 85 °C) test. It is thus concluded that the (K,Na)NbO₃-based composition containing excess zirconium is a good candidate material for nickel electrode multilayer ceramics.

The high-power piezoelectric characteristics of c-axis crystal-oriented (Sr,Ca)₂NaNb₅O₁₅ (SCNN) ceramics were studied by the constant-motional-current driving method, and compared with those of the randomly oriented ceramics superior to those of hard Pb(Ti,Zr)O₃ (PZT) ceramics. The c-axis crystal-oriented SCNN ceramic showed a large Lotgering factor of 0.98. The effective piezoelectric constant d₃₃^* was 260 pm/V, as large as those of hard PZT ceramics. In the 31-mode of the rectangular plate, the quality factor, Q, was five times larger than that of the randomly oriented ceramic, and almost constant at approximately 3300 up to the maximum vibration velocity of 1.84 m/s rms. The resonant frequency change was also stable up to a vibration velocity of 1.84 m/s rms. The change was approximately +0.05% in the driving range, which was much smaller than that of +0.8% of the randomly oriented ceramic. The high-power piezoelectric characteristics were also clarified by a comparison with the mechanical characteristics. Therefore, the highly c-axis crystal-oriented SCNN ceramics are good candidates for high-power piezoelectric applications in comparison with hard PZT ceramics.

The longitudinal and transverse wave velocities in lead zirconate titanate (PZT), lead titanate, and lead-free ceramics vs DC poling fields were measured using an ultrasonic precision thickness gauge with high-frequency pulse oscillation to evaluate elastic constants, such as Young's modulus and Poisson's ratio. With the enhancement of domain alignment with the increase in poling field, the longitudinal wave velocity increased and the transverse wave velocity decreased independently of the ceramic composition. It was found that there was an important factor for obtaining a high piezoelectricity regarding Young's modulus and Poisson's ratio, that is, the low Young's modulus and high Poisson's ratio in the cases of PZT, alkali bismuth titanate, and alkali bismuth barium titanate with morphotropic phase boundaries (MPBs), and alkali niobate without MPBs. Furthermore, the increase in planar coupling factor corresponds to the increase in Poisson's ratio at all compositions including lead-containing and lead-free ceramic compositions. It was possible to divide the ceramics on the basis of longitudinal and transverse wave velocities into three groups, namely, PZT and lead titanate modified by 2.5 mol % lanthanum, alkali bismuth titanate and lead titanate modified by 10 mol % lanthanum, and alkali niobate.

The dependence of the ferroelectric and piezoelectric properties of (1-x)(0.33BaTiO₃–0.67BiFeO₃)–xBi(Mg_1/2Ti_1/2)O₃ (x = 0, 0.05, 0.10, and 0.15) on Bi(Mg_1/2Ti_1/2)O₃ content x associated with microstructural changes is studied. From the behaviour of electric field-induced polarization and strain, polarization switching and depolarizing become easier as Bi(Mg_1/2Ti_1/2)O₃ content x increases. Remanent polarization and dielectric constant decrease, while polarization saturation field increases with increasing x. Microstructural observation reveals that Bi(Mg_1/2Ti_1/2)O₃ addition enhances the compositional fluctuation of BaTiO₃/BiFeO₃ ratio, which probably creates a nanometre-sized domain region with slightly BaTiO₃-rich composition. Since this nanometre-sized domain may cause relatively large responses of polarization and strain to the applied electric field, an appropriate amount of Bi(Mg_1/2Ti_1/2)O₃ enhances the electric field-induced strain, resulting in the largest piezoelectric response at x = 0.05. However, excessive Bi(Mg_1/2Ti_1/2)O₃ degrades polarization and strain characteristics, because a number of Ba(Fe_1-xMg_x/2Ti_x/2)₁₂O₁₉ grains are created as a secondary phase and cause the segregation of excess bismuth oxide phases with low dielectric constant into the boundaries of the ferroelectric/piezoelectric grains.

Potassium niobate-based ceramics with 0.1 wt % MnCO₃, K_(1+x)NbO₃+MnCO₃ 0.1 wt % (KN10000x+Mn, x = 0.0000–0.0010), were fabricated using KHCO₃ powder as a starting material. The KN10000x+Mn ceramics were basically fabricated using a conventional ceramic fabrication process and MnCO₃ powders were added at the milling stage after the calcination. High density ratios above 95% were prepared for the wide compositional range of excess K amount for KN10000x+Mn ceramics. From these results, Mn ions are thought to act as a sintering aid for KN ceramics. Mn-doped KN10000x ceramics also showed high resisitivities of approximately 10¹² Ω cm for the wide variety of x (10000x=0–9). Moreover, the electromechanical coupling factors k₃₃ for KN10000x+Mn had constant values of higher than 0.50.

A model experiment on the grain-size-related dielectric and ferroelectric properties of lead-free Li_0.04(Na_0.50K_0.50)_0.96NbO₃ piezoelectric ceramics has been carried out. Firstly, the size classification of calcined powders was achieved by a wet-type centrifugal separation technique to obtain size-classified powders with different mean particle sizes. Then, spark plasma sintering (SPS) under an identical condition at 960 °C for 10 min at a pressure of 80 MPa was performed for the size-classified powder sources to synthesize dense ceramics and control their mean grain sizes so that they ranged from 500 nm to approximately 5 µm. The results clearly allowed the distinguishing of different dielectric and ferroelectric properties on the basis of grain size. By increasing the grain size from 0.5 to 2.8 µm, the remanent polarization P_r gradually increases from 4.2 to 16.8 µC/cm², but a further increase in grain size to 4.8 µm causes a decrease in P_r to 9.2 µC/cm², while the coercive field E_c tends to increase with decreasing grain size. Our findings and the new technique to control grain size may stimulate further systematic investigation of grain-size-related properties for the development of lead-free alkali niobate piezoelectric ceramics showing excellent electrical properties.

We have investigated the molecular alignment structure of ferroelectric liquid crystals (FLCs) in a wide-gap cell for application to optical devices, such as an electrically controlled lens. The transformation of the smectic layer structure has been observed under an electric field, particularly under a low electric field in the wide-gap cell. We have attempted to suppress this transformation, which considerably degrades the optical performance of FLCs, by the polymer stabilization technique. As a result, we have found that the layer transformation can be suppressed successfully. However, the disarray of the FLC molecular alignment may occur owing to the deformation of polymer networks accompanied by FLC molecular reorientation caused by the application of an electric field.

Piezoelectric properties of ferroelectric Bi₄Ti₃O₁₂ (BiT) single crystals have been investigated by a resonance–antiresonance method. Large and high-quality single crystals of BiT were obtained via top-seeded solution growth under a high oxygen pressure of 0.9 MPa. The elastic and piezoelectric constants in the (11), (12), (13), and (26) modes for BiT single crystals have been determined for the first time. It is shown that BiT has a large d₂₆ constant of 79 pC/N and a large k₂₆ factor of 40%, indicating that BiT is a promising ferroelectric material for application to shear-mode piezoelectric devices.

The dielectric, elastic, and piezoelectric constants of langasite family single-crystal La₃Ta_0.5Ga_5.3Al_0.2O₁₄ (LTGA) were measured by combing plane-wave ultrasonic microspectroscopy (PW-UMS) technology with the resonance–antiresonance method in a range from room temperature to 1000 °C. The influence of dielectric loss at high temperatures on resonance and antiresonance frequencies was discussed. At room temperature, the piezoelectric constants d₁₁ and d₁₄ were 6.62 and -4.65 pC/N, respectively. d₁₁ increased to 7.5 pC/N at 1000 °C. The electromechanical coupling factor k₁₂ was about 16.8% in the entire temperature range. All the necessary parameters of the LTGA crystal for acoustic wave applications at high temperatures were determined in this research.

The relationship between piezoelectric loss (tan δ_P) and dielectric loss (tan δ_E) in the converse piezoelectric effect in piezoelectric ceramics was investigated theoretically and experimentally. The theoretical consideration was based on the assumption that strain should be proportional to polarization without phase delay in both the intrinsic contribution due to lattice deformation and the extrinsic contribution due to domain wall motion. It was expected that the piezoelectric loss in the converse piezoelectric effect should be identical to the dielectric loss. In order to experimentally verify the identicalness between the losses, the immittance curves of the piezoelectric response of various Pb(Zr,Ti)O₃-based ceramic resonators were fitted if the piezoelectric loss tan δ_P (1) is equal to zero, (2) exists as the independent variable, and (3) is the same as the dielectric loss tan δ_E. The observation result clearly proved that tan δ_P is identical to tan δ_E. This identicalness was also demonstrated by analyzing the phase angle of vibration velocity in mechanical response.

An animal health monitoring system and a wireless sensor node aimed at preventing the spread of animal-transmitted diseases and improving pastoral efficiency which are especially suitable for chickens, were developed. The sensor node uses a piezoelectric microelectromechanical system (MEMS) device and an event-driven system that is activated by the movements of a chicken. The piezoelectric MEMS device has two functions: a) it measures the activity of a chicken and b) switches the micro-control unit (MCU) of the wireless sensor node from the sleep mode. The piezoelectric MEMS device is required to produce high output voltages when the chicken moves. However, after the piezoelectric MEMS device was reflowed to the wireless sensor node, the output voltages of the piezoelectric MEMS device decreased. The main reason for this might be the loss of residual polarization, which is affected by the thermal load during the reflow process. After the reflow process, we were not able to apply a voltage to the piezoelectric MEMS device; thus, the piezoelectric output voltage was not increased by repoling the piezoelectric MEMS device. To address the thermal load of the reflow process, we established a thermal poling treatment, which achieves a higher temperature than the reflow process. We found that on increasing the thermal poling temperature, the piezoelectric output voltages did not decreased low significantly. Thus, we considered that a thermal poling temperature higher than that of the reflow process prevents the piezoelectric output voltage reduction caused by the thermal load.

In this paper, we address the fabrication and characterization of bimorph structures with relatively thick double-layered Pb(Zr,Ti)O₃ (PZT) thin films. The PZT/PZT layers are deposited by RF magnetron sputtering. Hysteresis loops of polarization and electrical field for the top and bottom PZT thin films revealed good ferroelectric characteristics with remanent polarization at approximately 20 µC/cm² and a coersive electric field of about 100 kV/cm. The vibration tests of fabricated bimorph cantilevers during electrical voltage application revealed a twofold displacement compared with single layer driving, and the piezoelectric coefficient value d₃₁ is estimated to be 13 pm/V. The residual stress difference between the top and bottom layers after the annealing process is calculated to be -0.32 MPa. For a further thickening of the bimorph structure, 6-µm-thick PZT/PZT is also sputtered. The thicker bimorph has a smaller residual stress difference, -30 MPa, between the two layers prepared without the annealing process. The evaluated results demonstrate that the PZT/PZT bimorph structures are applicable to micro-electromechanical systems (MEMS) devices.

A shear-mode inkjet head utilizing alkaline niobate-based lead-free piezoelectric ceramics has been developed. A prototype inkjet head with a nozzle density 150 dots per inch (dpi) was achieved on a grayscale of eight levels with a minimum ink droplet ejection of 6 pl. Furthermore, the inkjet head with a nozzle density of 300 dpi was achieved on a grayscale of four levels with a minimum ink droplet ejection of 3 pl. Although the prototype inkjet head required a high voltage of approximately twice the driving voltage of the inkjet head using lead zirconate titanate (PZT) piezoelectric ceramics, the grayscale can be realized by a multidrop method. Thus, the alkaline niobate-based lead-free piezoelectric ceramics can be used to replace PZT ceramics as shear-mode actuators for inkjet heads.

Synthetic piezoelectric polymer films produced from petroleum feedstock have long been used as thin-film sensors and actuators. However, the fossil fuel requirements for synthetic polymer production and carbon dioxide emission from its combustion have raised concern about the environmental impact of its continued use. Eco-friendly biomass polymers, such as poly(L-lactic acid) (PLLA), are made from plant-based (vegetable starch) plastics and, thus, have a much smaller carbon footprint. Additionally, PLLA does not exhibit pyroelectricity or unnecessary poling. This suggests the usefulness of PLLA films for the human–machine interface (HMI). As an example of a new HMI, we have produced a TV remote control using a PLLA film. The intuitive operation provided by this PLLA device suggests that it is useful for the elderly or handicapped.

To realize a new piezoelectric chiral polymer actuator, we studied the motion induced by the shear piezoelectricity of a poly(L-lactic acid) (PLLA) film under the application of an ac voltage. First, PLLA was subjected to a supercritical CO₂ treatment to change its high-order structure, resulting in an improvement in its piezoelectricity. Then, we designed a PLLA film roll transducer, which consisted of a piece of the treated PLLA film rolled into a long thin roll. To demonstrate the transducer, we placed it vertically on a fixed stand. A plastic hemispherical container was placed on the upper end face of the transducer. It was found that the container rotated smoothly in the counterclockwise direction when an ac voltage was applied. We emphasize that no special complex mechanical parts were used in this study.

To realize a new polymer sensor fabricated from a piezoelectric chiral polymer fiber, we attempted to detect the response signal induced by the shear piezoelectricity of the chiral polymer poly(L-lactic acid) (PLLA) under the application of stress and strain, and we confirmed that the piezoelectric response signal was sufficiently large for use as a sensor signal. We then prepared a left-hand helical torsion coil (PLLA fiber left-hand coil), which was formed by drawing a PLLA fiber ten times. It was observed that, when twisted and released suddenly, the coil exhibited a torsion vibration, and we confirmed that the piezoelectric response signal followed the torsion vibration. Next, we prepared a system in which a PLLA fiber coil was linked to a personal computer used for simple image processing. The PLLA fiber left- and right-hand coils were placed on the arm of a subject, and the inward rotation and outward rotation of the forearm and upper arm were measured. Finally, using this system, we were able to visualize the rotation of the forearm and upper arm.

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO₃ is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [E_f(V_O)] in Zr-doped and undoped BaTiO₃ was performed. The E_f(V_O) of Zr-doped BaTiO₃ was higher than that of undoped BaTiO₃ because the valence of Ti in undoped BaTiO₃ easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO₃. We also prepared undoped (BaTiO₃) and Zr-doped (BaZr_0.05Ti_0.95O₃) ceramic samples sintered under reducing atmosphere (T = 1573 K p_O2 = 10^-13 MPa). BaZr_0.05Ti_0.95O₃ remained an insulator, but BaTiO₃ showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.

AgNbO₃ has been reported to undergo an antiferroelectric–ferroelectric phase transition between two orthorhombic phases (labeled M₂ and M₁) on cooling below ∼340 K. However, the phase transition mechanism is still not well understood, with different space groups proposed for the structure on the basis of different experimental techniques. Here, we report the first-principles calculations of low-temperature phases of AgNbO₃ using the projector augmented wave method based on the density functional theory. The calculated phonon dispersion curve for the antiferroelectric Pbcm structure shows that no soft mode is evident over all wave vectors, indicating that the structure is dynamically stable. The M₂–M₁ transition of AgNbO₃ thus cannot be explained on the basis of these results. Further calculations are needed to uncover the precise phase transition mechanism for this compound.

A model of coexistence states near the morphotropic phase boundary (MPB) in perovskite-type ferroelectric crystals was studied using a simplified simulation based on the Landau–Ginzburg-type free energy functional. It was found that, even when no imperfection causing the random field exists, a stable phase and a metastable phase coexist near MPB. The coexistence state in the engineered domain configuration near MPB was also found.

As preliminaries of a microscopic theory for displacive phase transition, the first-order transition is investigated within a phenomenological study that provides a good explanation of experimental results on the electric field dependence and pressure effect in relaxor ferroelectrics. The morphotropic phase boundary (MPB) region in mixed perovskite oxides is described in the same phase diagram corresponding to individual perovskite oxides with successive phase transitions. On the basis of the calculated field-dependent phase transitions, the origin of the MPB is examined in comparison with that in the case of BaTiO₃ with the first-order displacive transition.

High-energy synchrotron radiation powder diffraction experiments have been carried out to investigate the crystal structure of solvothermally synthesized KNbO₃ (KN)/BaTiO₃ (BT) nanocomposite ceramics in which a ceramic grain consists of a BT nanoparticle thinly coated with KN crystals through the heteroepitaxial interface. Rietveld analysis reveals that the ceramic grain has the core/multishell structure consisting of a BT core and distorted BT and KN multishells. BT is gradually distorted in the large region to form the interface with KN from the tetragonal structure at the core toward the cubic structure at the boundary between BT and KN. The variations of the volume of the distorted interface region of BT and the dielectric property of the ceramics show similar trends to the variation of KN/BT molar ratio, which suggests that the electrically soft interface of BT nanoparticles governs the dielectric properties of the ceramics.

A local structure analysis of Bi₂WO₆ was performed by high-energy X-ray atomic pair-distribution function (PDF) analysis. We found a deviation between the local and average structures owing to the different coherence lengths between the Bi₂O₂ and WO₆ layers. Bi atoms were displaced toward the b-axis of the orthorhombic Pca2₁ structure. The local off-center shift of Bi atoms coupled with the thermal factor but not with the average structure and thus was neglected. The coherence length of the Bi₂O₂ layer increased with increasing temperature and spread in the whole crystal when the average structure changed from the Pca2₁ structure to the Aba2 structure.

Scanning nonlinear dielectric microscopy is a powerful technique for measuring the domain structure of ferroelectrics. We observed congruent LiTaO₃ and found the marked enhancement of nonlinear dielectric "constants" when the applied tip–sample voltage exceeded a particular threshold value. This is due to domain nucleation activated by a huge electric field under the tip. Moreover, low frequencies (less than a few hundred Hz) did not enhance the nonlinearity. An effectively lower electric field caused by ion conduction in the sample under the tip is a possible reason for the frequency-dependent characteristics of the enhanced nonlinearity for the applied voltage.

Preisach modeling of a field-induced nonlinear strain of a ferroelectric material was carried out. A hysteron having a tristable property was proposed. The three stable states correspond to the three stable polarization states of a ferroelectric material. The domain evolution under an electric field was calculated. Finally, the electric-field-induced strain of ferroelectric ceramics was calculated and compared with experimental values. The proposed model enables the description of major and minor strain butterfly loops of ferroelectric materials.

Changes in ferroelectric and structural antiphase domain structure by the partial substitution of nonmagnetic Ti⁴⁺ ions at the Mn site were investigated carefully by electron diffraction, dark-field imaging, and high-resolution lattice imaging experiments. The ferroelectric and structural antiphase domains are revealed to be mutually interlocked in YMnO₃ and, on the other hand, when x was increased up to x∼0.30 in YMn_1-xTi_xO₃, the ferroelectric domains disappeared and the size of the structural antiphase domains decreased to approximately 10 nm at x∼0.30. High-resolution lattice images clearly demonstrate the coexisting state of nanodomains characterized by the modulated structure due to the structural trimerization and the nonmodulated structures. Our experimental results suggest that a partial substitution of Ti⁴⁺ ions suppressed the ferroelectric displacement along the [001] direction and the correlation length of the Mn³⁺ trimerization decreased.

Nd-doped BiFeO₃ (BNF) thin films were fabricated on SrRuO₃ (SRO)-coated (100) Nb-doped SrTiO₃ substrates by pulsed laser deposition, and nondoped BiFeO₃ (BFO) thin films were also fabricated similarly for comparison. Then, Nd-doping effects on ferroelectric and photovoltaic properties were evaluated. Polarization-induced photovoltaic effects were observed in both the BFO and BNF solar cell structures with top and bottom electrodes under intense laser illumination. Using Au top electrodes, enhanced photovoltaic properties were observed in the BNF cell compared with the BFO cell. To improve the photovoltaic properties of the BNF cell, instead of the Au top electrodes, In–Sn–O (ITO) top electrodes were employed for the BNF cell. As a result, the photovoltaic properties were found to be markedly improved, resulting in an open circuit voltage of 0.81 V and a short circuit current density of 12.1 mA/cm².

The influences of LiF and CaTiO₃ addition on the microwave dielectric properties of MgO ceramics were investigated in this study. The LiF was effective in reducing the sintering temperature of MgO without a detrimental effect on the quality factor (Q·f). The 0.05 mol LiF-added MgO ceramics were sintered at a temperature of 950 °C which resulted in dielectric constant (ε_r) and Q·f values of 9.6 and 215,000 GHz, respectively, though the temperature coefficient of resonant frequency (TCf) had a large negative value of -63.5 ppm/°C. In order to achieve near-zero TCf values, (0.95-x)MgO–xCaTiO₃–0.05LiF ceramics were also investigated and the formation of a secondary phase in MgO–CaTiO₃–LiF ceramics was not observed in the X-ray powder diffraction profiles. Although the Q·f values of the ceramics were lowered by CaTiO₃ addition, a near-zero TCf was obtained at x = 0.05 (TCf= -3.2 ppm/°C). The ε_r and Q·f values of the 0.90MgO–0.05CaTiO₃–0.05LiF (x = 0.05) ceramic were 12.7 and 93,500 GHz, respectively. From these results, it is considered that CaTiO₃-added (0.95-x)MgO–xCaTiO₃–0.05LiF ceramics are appropriate candidates as high-Q low-temperature cofired-ceramics (LTCCs).

Recent developments in wireless communications have been expanded to millimeter waves for the high speed and the high rate transmission. Dielectrics with an ultrahigh quality factor Q and low dielectric constant ε_r are desired. Silicates are good candidates for millimeter wave dielectrics because of their low ε_r. Diopside (CaMgSi₂O₆) is one of the silicates with a chain SiO₄ structure and a low ε_r. In this study, we focused on the fabrication conditions of diopside by the means of solid state reactions. The best ceramic of diopside with dielectric properties of ε_r = 7.6, Q ·f = 121,381 GHz and TCf= -66 ppm/°C was obtained by means of sintering a fine powder fabricated under the following conditions. Fine calcined grain powders were fabricated using fine raw materials with more than 99.9% purity, milling well for 24 h using ZrO₂ balls with ca. 5 mmφ, and calcining at 1200 °C for 3 h. The powder was a fine isolated powder without necking with ca. 0.3 µm size, as observed by scanning electron microscopy (SEM), and the specific surface area was ca. 3 m²/g, corresponding to ca. 0.66 µm grain sizes, as determined by the Brunauer–Emmett–Teller (BET) method. The relative density of sintered ceramics with mainly diopside composition formed by sintering the high-density green pellet applied cold isostatic pressing (CIP) at 1300 °C for 3 h was ca. 97%. The necking at 1250 °C was formed by a eutectic liquid on the SiO₂–MgO binary system, which is formed by residual SiO₂ in the core of low SiO₂ materials.

A novel measurement method is proposed to evaluate the complex permittivity of material by using a cylindrical cavity resonator. The conventional cavity resonator methods have been based on the simple electromagnetic field analysis, and a rodlike sample should be loaded all the way from the top to the bottom of the resonator. However, the method proposed in this paper employs an accurate and efficient hybrid electromagnetic analysis method for the evaluation of materials and removes the restriction on the size of the sample materials. The radius and length of the sample are chosen considering the electrical characteristics of the sample, and the fact allows the expansion of the application range of the evaluation method to the materials with higher permittivity and/or higher loss. Also, the sample is not loaded in the insertion opening of the resonator in the proposed method. Therefore, it prevents the leakage of electromagnetic fields through opening and improves the accuracy of the evaluation of material with higher permittivity and/or higher loss. Complex permittivities of a few samples of ceramics with high permittivity and lossy electromagnetic absorber are measured in a microwave range to show the validity of this method.

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