Table of contents

The 2020 International Conference on Defects in Insulating Materials (ICDIM2020) was the 20th edition of a series that began in 1956 at Argonne, USA, with the meeting "Color Centers in Alkali Halides". International conferences (ICDIM) take place every four years and are alternated with Europe-specific conferences (EURODIM). The series is a broad international forum on the science and technology of defect-related phenomena in crystalline and amorphous wide band-gap materials. Recent ICDIM Conferences were held in South Africa (2000), Latvia (2004), Brazil (2008), USA (2012) and France (2016). Because of the COVID-19 pandemic, the conference was held online. These proceedings represent a sample of the work presented at the conference.

We are grateful to the IT department of the Federal University of Sergipe, Brazil, for their help in hosting the website and YouTube channel of the conference.

List of ICDIM committees, Programme Advisory Committee, International Advisory Committee are available in this Pdf.

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

• Type of peer review: Single Anonymous

• Conference submission management system: Morressier

• Number of submissions received: 19

• Number of submissions sent for review: 18

• Number of submissions accepted: 16

• Acceptance Rate (Submissions Accepted / Submissions Received × 100): 84.2

• Average number of reviews per paper: 2.5

• Total number of reviewers involved: 29

• Contact person for queries:

Name: Mário Ernesto Giroldo Valerio

Email: megvalerio@academico.ufs.br

Affiliation: Federal University of Sergipe, Physics Department

The peculiar photoluminescence characteristics of radiation-induced colour centres in lithium fluoride (LiF), well known for applications in optically-pumped tuneable lasers and broad-band miniaturised light-emitting photonic devices operating at room-temperature, are under exploitation in passive imaging detectors and dosimeters based on visible radiophotoluminescence in LiF crystals and polycrystalline thin films. Their high intrinsic spatial resolution, wide dynamic range and large field of view, combined with easy handling, ambient-light operation and no development need, allow to successfully extend their use from X-ray imaging to proton-beam advanced diagnostics and dosimetry, even at those low dose values that are typical of hadrontherapy. After exposure, the latent images stored in LiF as local formations of F₂ and F₃⁺ aggregate defects are read with an optical fluorescence microscope under illumination in the blue spectral range. Their visible emission intensity was found to be linearly proportional to the dose over at least three orders of magnitude, so that bi-dimensional LiF solid-state dosimeters based on spectrally-integrated radiophotoluminescence reading can be envisaged. Taking advantage of the low thickness of LiF thin films, transversal proton beam dose mapping was demonstrated at low proton energies, even at high doses. Recent results and advances concerning LiF crystals and polycrystalline thin film characterisation in the linearity range are presented and discussed with the aim of highlighting challenges related to increasing the LiF film detector radiation sensitivity to both particles (protons) and photons (X-rays), although therapeutic dose values typical of clinical radiotherapy are still a big challenge.

The doping of MgF₂ with the 229 isotope of Th is of interest in the development of nuclear clock devices. This paper describes atomistic modelling of MgF2, its intrinsic defects and Th doping, and compares the results with a recent study using Density Functional Theory (DFT).

Lithium-sulfur (Li-S) batteries are a popular Li-ion alternative because they have a high capacity (1672 mAhg1) and energy density (2500 Wh kg1) while being inexpensive, environmentally friendly, and lightweight [1–3]. During cycling, Li/S is hampered by the low conductivity of S and the solubility of intermediary polysulfide species. Se and mixed SexSy have been shown to offer an appealing new class of cathode materials with good electrochemical performance in both Li and Na ion processes [4]. These new Se and Li/SexSy electrodes can cycle at ambient temperature, unlike existing Li/S batteries, which can only operate at high temperatures. Room temperature cycling is possible using Li/SexSy electrodes. Empirical interatomic potentials of Li₂S were generated and confirmed against existing experimental and predicted structure, elastic properties, and phonon spectra in order to analyse large systems and the impact of temperature effectively. Complex high-temperature changes including Li₂S melting were also replicated, as predicted by molecular dynamics simulations.

The emission spectrum of electron intraband luminescence was calculated for a dielectric crystal with conduction band consists of multiple parabolic branches. This shape of this spectrum adequately correspond to the CsI experimental spectra in the photon energy region ≥ 1.2 eV. The calculated total quantum yield of intraband luminescence of CsI is about 78 photons collected by the silicon photomultiplier per 1 MeV of deposited energy of ionizing radiation. This value is about two times higher than the experimental one, the difference is due to the simplification of the model. It was shown that characteristic times of intraband luminescence are about 1 ps.

La-modified PbZrTiO₃ ferroelectric ceramics with Pb_0.92La_0.08(Zr_0.686Ti_0.294)O₃ nominal composition were obtained via the conventional solid-state reaction method, by considering different PbO excess (5, 10 and 15 mol %). The structural properties, were investigated from X-ray diffraction (XRD) and Raman Spectroscopy techniques, both at room temperature. Results confirmed the formation of the perovskite structure with rhombohedral symmetry (R3m space-group) for all the samples. The dielectric properties were also investigated, from the temperature dependence of the dielectric response, and results revealed the characteristic response of ferroelectric materials for all the compositions. The obtained very broad peak in the maximum dielectric permittivity, around Tm (~107°C), suggests the diffuse character of the ferroelectric-paraelectric phase transition.

The structural properties of Ba₂YNbO₆ were adjusted and compared with experimental data through an interatomic potential that was optimized here and is based on a model known as the shell model used in this work for oxygen ions. Intrinsic and extrinsic defects were calculated based on the minimization of the crystal lattice energy through computational modeling. Calculations showed that rare earth ions prefer to incorporate the Y³⁺ site and Mn⁴⁺ the Nb⁵⁺ site, thus being more energetically favorable.

The results reported herein were motivated by the potential application of combined optically stimulated (OSL) and thermoluminescence (TL) measurements for separation between the beta and neutron dose components in mixed neutron-beta radiation fields. The advantages of OSL/TL are two-fold: (i) The OSL and TL readout can be carried out on the same sample and (ii) the greater efficiency of OSL to high ionization density (HID) radiation due to the excitation of F₂ and F₃⁺ centers. The beta calibration coefficients for LiF:Mg,Ti (TLD-700) were measured using a ⁹⁰Sr/⁹⁰Y source calibrated at the Soreq Nuclear Research Center nuclear facility. The estimation of the neutron calibration coefficients was carried out by irradiation with broad beam fast neutrons of median energy 5 MeV and a quasi-monoenergetic neutron field of mean energy 14.8 MeV at the Physikalisch Technische Bundenanstalt. The preferential excitation of OSL following HID irradiation has been demonstrated.

The cubic garnet-type Li₇La₃Zr₂O₁₂ is an eminent candidate for next-generation solid state battery technology due to its thermal stability and high ionic conductivity. As such, its operation mechanisms need to be thoroughly understood, particularly focusing on the structural instability challenge reported to occur at lower temperatures. Herein, the statistical sampling capability of molecular dynamics simulations is employed during the investigation of fundamental structural, kinetic and thermodynamic properties emanating its subjection to pressure and temperature. Systematic induction of pressure yielded transition of the tetragonal phase to the cubic phase at 2 GPa pressure. The lattice parameters for the cubic and tetragonal phases, acquired in the current study are within 0.38 % agreement with literature. Furthermore, the XRD graphs confirm varying phases under different pressure conditions. The temperature phase diagram for 0 GPa structure agrees well with the literature trends and interestingly, the 2 GPa structure retained the cubic phase at various temperatures and confirmed in the XRDs and temperature phase diagram. Interrogatio of LaO₈ dodecahedral and ZrO₆ octahedra demonstrated no significant variations in bond lengths and bond angles giving a good indication for the regulation of Li⁺-transport channel size in the 2 GPa structure. Efforts in this study are a preliminary stage to fully understanding the thermodynamic impact as a structural modification avenue pending further investigations.

Developing new battery technologies to sustain the ever-growing demand for energy storage constitutes one of the greatest scientific and societal challenges of the century. Lithium-ion batteries (LIBs) are frequently used at the moment as energy storage, and they are used to power millions of portables electronics, electric vehicles, and are even seeing introduction into the electric grid. But LIBs are facing some challenges such as safety, durability, uniformity and cost. A technology that has the potential to alleviate resource issues with Li-ion systems and further increase the energy density is Mg²⁺ intercalation systems. Replacing Li with safer and earth-abundant Mg has the advantage of doubling the total charge per ion, which result in larger theoretical volumetric capacity compared with LIB. First principle based calculations were used to investigate the stability of discharge products of solid electrolytes in the magnesium-ion battery. We found that MgSc₂S₄ and MgSc₂Se₄ structures are stable semi-conductors due to the band gap observed in the density of states. No negative vibrational frequencies are observed along all direction in the phonon dispersion curves which indicate stability. The calculated elastic constants indicate that the structures are mechanically stable. The results of this paper aimed to give an insight into the stability of solid electrolytes and to provide inspiration for future research in magnesium-ion batteries.

The layered transition metal oxides formulated LiMO₂ (M: Mn, Ni and Co) are a state-of-art cathode material for lithium-ion batteries. They have attracted considerable attention due to their capability to optimize the capacity, cyclic rate, electrochemical stability, and lifetime. This paper reports the DFT+U calculations performed on LiMnO₂, LiNiO₂ and LiCoO₂ materials. The heats of formations predict that the LiNiO₂ is the most thermodynamically stable material while the LiMnO₂ is the least thermodynamically stable material. The energy bandgap for LiNiO₂ is relatively small suggesting that the material is high in conductivity. Conversely, the energy bandgaps of LiMnO₂ and LiCoO₂ are relatively wide suggesting that the materials are low in electrical conductivity. All independent elastic constants are positive and satisfying the mechanical stability criterion. Lastly, the phonon dispersion curves display imaginary vibration along high symmetry direction for LiCoO₂. However, the material is inferred stable with support from the elastic constants. The LiNiO₂ is the most stable material and LiCoO₂ is the least stable material.

Electro-ceramics based on the KNbO₃ ferroelectric system were synthesized from the solid-state reaction sintering method. In particular, the electrical properties have been investigated at room temperature in the (1−x)KNbO₃−xBaNi_1/2Nb_1/2O_3−δ (KBNN) solid-solution. The dielectric relaxation mechanisms have been analyzed as a function of the oxygen vacancy (δ) concentration and the frequency dispersion of the complex dielectric permittivity was analyzed in a wide frequency range. The obtained results were discussed within the framework of the current models reported in the literature for the dielectric relaxation processes.

The structural properties in Ag_1−xLa_xNbO₃ ceramics (where x = 0.005) have been systematically investigated at room temperature by using X-ray diffraction (XRD) technique and Raman spectroscopy. The studied sample has been synthesized via the conventional solid-state reaction method. The XRD result confirmed the formation of a single-phase with orthorhombic crystal structure for the studied composition. The signature of the Raman spectrum revealed structural modification with the inclusion of the doping element, with respect to the pure AgNbO₃ system, showing additional modes in the middle wavenumbers range (570–758 cm⁻¹).

Bioactive ferromagnetic glass-ceramics composites have been prepared through the combination of the quenching and solid-state reaction (SSR) sintering methods, viewing their integration in biomedical applications. The material under study consists of a glassy system with the chemical formula (94-2x)SiO₂−xNa₂O−xCaO-6P₂O₅, which acts as host-matrix for the magnetic phase (strontium ferrite). The samples were obtained by a modified incorporation technique, where the magnetic phase, previously synthetized by the SSR method, was added to the glass-matrix in desired proportions. The physical properties were investigated considering the analysis of the X-ray diffraction as well as Raman spectroscopy techniques, both performed at room temperature. Results revealed the formation of partially crystallized bioglass-ceramics, with a strong influence of the magnetic phase on the crystallization kinetics, which suggests the obtained bioactive composites promising materials for clinical treatments.

In this study, three photoelectrodes with bismuth vanadate (BVO) and bismuth oxide (BO) films were deposited on an ITO coated glassy substrate using three different routes. Both photoelectrodes were photoactive when irradiated by light. Notably, the photoelectrode with the BVO–1/BVO–2/BO film showed improved photoelectrochemical performance compared to the BVO–1 and BVO–1/BVO–2 films, due to the synergies involved in the process of separation/transportation of the photogenerated charges. The results indicate the promising use of this material for the clean production of solar fuels.

In this work we performed experimental analyses of the dose-response curves of natural alexandrite, using thermoluminescence (TL) and optically stimulated luminescence (OSL). The natural alexandrite crystals from Bahia, Brazil, were pulverized and the optical absorption measurements were carried out in the range of 200 to 800 nm, comparing a non-irradiated sample with a 10 Gy beta irradiated one. OSL and TL measurements were performed using the Risø equipment (model DA-20) with irradiation doses from 1 to 5 Gy. Glow curve analysis was done using GlowFit software for TL, and R Studio software for OSL measurements. The irradiated sample (10 Gy) shows an absorption spectrum similar to the non-irradiated one, containing the same bands. The samples of natural alexandrite showed a linear dose-response for both OSL and TL measurements. From the TL and OSL analyses, it was possible to infer a correlation between the slow OSL component with the most intense TL peaks of alexandrite.

Lanthanum modified BiFeO₃ thin films were prepared via the sol-gel method and deposited through the dip-coating technique on ITO coated substrates. The structural properties were investigated at room temperature from X-ray diffraction as well as Raman spectroscopy. Results confirm the formation of the perovskite structure without secondary phases, thus corroborating the high-quality of the obtained thin films. Well-defined and nanometric scale grains have been obtained from atomic force microscopy, revealing indeed crack-free surfaces. From the technological point of view, this result is very important since residual stresses promoted by surface cracks led to additional conduction behavior, which could affect the real electric response of the sample to be used in electronic devices.