Pressure-induced phase transition of Bi2Te3 into the bcc structure

The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been studied by synchrotron x-ray diffraction measurements at room temperature using a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is denoted as phase IV, and this phase apperars above 14.5 GPa. Upon releasing the pressure from 29.8 GPa, the diffraction pattern changes with pressure hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc structure can explain the phase IV peaks. We assumed that the structural model of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms are distributed in the bcc-lattice sites with space group Im-3m. The results of Rietveld analysis based on this model agree well with both the experimental data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic% tellurium) binary system.Comment: 12 pages, 5 figure

Effect of Substrates on the Physicochemical Properties of Li7La3Zr2O12 Films Obtained by Electrophoretic Deposition

Thin film technology of lithium-ion solid electrolytes should be developed for the creation of all-solid-state power sources. Solid electrolytes of the Li7La3Zr2O12 (LLZ) family are one of the promising membranes for all-solid-state batteries. LLZ films were obtained by electrophoretic deposition on Ti, Ni and steel substrates. The influence of different metal substrates on microstructure, phase composition and conductivity of the LLZ films after their heat treatment was studied. It was shown that the annealing of dried LLZ films in an Ar atmosphere leads to the transition from tetragonal modification to a low-temperature cubic structure. It was established that an impurity phase (Li2CO3) was not observed for LLZ films deposited on Ti foil after heat treatment, in contrast to films deposited on Ni and steel substrates. The highest lithium-ion conductivity values were achieved for the LLZ films annealed at 300 °C, 1.1 × 10−8 S cm−1 (at 100 °C) and 1.0 × 10−6 S cm−1 (at 200 °C). © 2023 by the authors.Russian Academy of Sciences, РАН: 122020100210-9The research was funded by the Russian Academy of Sciences (No. 122020100210-9, (IHTE UB RAS))

Electrophoretic Deposition and Characterization of Thin-Film Membranes Li7La3Zr2O12

In the presented study, films from tetragonal Li7La3Zr2O12 were obtained by electrophoretic deposition (EPD) for the first time. To obtain a continuous and homogeneous coating on Ni and Ti substrates, iodine was added to the Li7La3Zr2O12 suspension. The EPD regime was developed to carry out the stable process of deposition. The influence of annealing temperature on phase composition, microstructure, and conductivity of membranes obtained was studied. It was established that the phase transition from tetragonal to low-temperature cubic modification of solid electrolyte was observed after its heat treatment at 400 °C. This phase transition was also confirmed by high-temperature X-ray diffraction analysis of Li7La3Zr2O12 powder. Increasing the annealing temperature leads to the formation of additional phases in the form of fibers and their growth from 32 (dried film) to 104 μm (annealed at 500 °C). The formation of this phase occurred due to the chemical reaction of Li7La3Zr2O12 films obtained by electrophoretic deposition with air components during heat treatment. The total conductivity of Li7La3Zr2O12 films obtained has values of ~10−10 and ~10−7 S cm−1 at 100 and 200 °C, respectively. The method of EPD can be used to obtain solid electrolyte membranes based on Li7La3Zr2O12 for all-solid-state batteries. © 2023 by the authors.Russian Academy of Sciences, РАНThis research was funded by the Research Program № 122020100210-9 (IHTE UB RAS), Russian Academy of Sciences, Ural Branch, Russia

Management of academic staff activity: modeling and prediction of rating system indicators

This paper deals with the problem of constructing a system of rating indicators for stimulating the work of the academic staff in higher educational institution. Many areas of teacher activity (for example, educational, scientific, international, etc.) laid the basis of selection the groups of indicators in the system. Social challenge in improving the quality of educational services determines the relevance of research in the field of modeling and prediction of indicators which characterize the work of high school teacher. To predict the dynamics of the structure of the rating indicators in the system, the authors introduced the concept of drift and variability of each group. Using informational hypercube for the structure of input data allowed authors to take into account the individual characteristics of each parameter included in a mathematical model to describe the rating indicators. To make the prediction of the structure and values of rating system indicators the authors introduced the concept of drift. Drift of indicators takes into account the introduction of new indicators, the removal of existing indicators, and movement of indicators between the groups. In the article, authors introduced a novel quantitative indicator of group variability. The value of this indicator determines the prediction strategy of the teacher work in higher school in the future period. To predict the total amount of stimulating, the complex technique offered and it includes four modules: modeling values within the existing range in the previous period; modeling new index value based on the assumptions introduced using a random number generator; exclusion a range of values of deleted indicators; modeling new values based on the study of the modern trend of indicators. The presence of flexible information structure in the form of a hypercube and complex mathematical model allowed authors to carry out numerical simulation for predicting the values of individual and group indicators. During the experiment, the structural stability of values is detected, and it does not lead to a drastic changing of the quantitative ratio between the groups of indicators

Features of Electronic States in the Vicinity of Band Gap and Atomic Structure of Ta- and Nb-Doped Li7La3Zr2O12

Received: 25.04.2024. Revised: 05.05.2024. Accepted: 05.05.2024. Available online: 06.05.2024.Li7La3Zr2O12 is one the most promising materials for Li-conducting solid electrolytes. The incorporation of Ta5+ and Nb5+ into the Zr4+ sites stabilizes its cubic structure and significantly enhances Li-conductivity, due to the formation of Li vacancies. In this research, we have studied the band gap features of Ta and Nd-doped Li7La3Zr2O12. Our findings indicate that Nb ions are present not only in the +5 valence state, but also in the +4 state, leading to the formation of oxygen vacancies. In the case of the Tadoping, such an effect was not observed. This could be the reason for the approximately one order of magnitude higher lithium conductivity observed in the case of the Ta doping, in comparison to the Nb doping.This work (except NMR measurements and NMR data analysis) was funded by the Russian Science Foundation (grant no. 22-73-00261), https://rscf.ru/en/project/22-73-00261/.This work was performed using equipment of the Shared Access Center “Composition of Compounds”. NMR measurements and NMR data analysis were performed by Germov A.Yu. in M.N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences (topic “Function”)

Features of Forming a Cubic Li7La3Zr2O12 Film by Tape Casting

Thin films of Li7La3Zr2O12 solid electrolyte were obtained by tape casting.The optimal heat treatment mode without films’ deformation was proposed.The highest conductivity values were observed for the Li7La3Zr2O12 film annealed at 800 °С – 1.5·10–5 S·cm–1 at 215 °С.Received: 13.10.23. Revised: 07.11.23. Accepted: 17.11.23. Available online: 21.11.23.Currently, interest to lithium and lithium-ion all-solid-state power sources is rapidly growing all over the world. However, several issues should be addressed before all-solid-state batteries production: high resistance values of the solid electrolyte membrane and poor contact between electrolyte and electrode materials. The transition to thin-film technologies is one of the promising ways to solve these problems. Tape casting can be proposed to obtain thin-film solid electrolytes. In this research, the features of the structure formation, morphology and lithium-ion conductivity of Li7La3Zr2O12 films were investigated. Li7La3Zr2O12 films with the thickness of 35 μm were obtained by tape casting on Ni substrate. The influence of organic components’ content on homogeneous coatings formation was established. Heat treatment conditions for dried films were chosen based on differential scanning calorimetry and optical dilatometry. Phase change from tetragonal to cubic modification occurs after annealing the Li7La3Zr2O12 films at 700 °C and higher. The annealed Li7La3Zr2O12 films have developed surface, which can lead to improved contact between the solid electrolyte and an electrode in an electrochemical cell. Li7La3Zr2O12 films annealed at 800 °C have the highest lithium-ion conductivity values (2.5·10–7 and 1.5·10–5 S·cm–1 at 90 and 215 °С, respectively). The technology of Li7La3Zr2O12 films formation with the thickness of ~23 μm by tape casting was developed.This research was funded by the Research Program No. 122020100210-9 (IHTE UB RAS), Russian Academy of Sciences, Ural Branch, Russia.The research has been carried out with the equipment of the Shared Access Center “Composition of Compounds” at the IHTE UB RAS

Synthesis and Research of Alumina Ceramics Properties

Received: 27.10.2020. Revised: 18.12.2020. Accepted: 18.12.2020. Available online: 21.12.2020.This article belongs to the PCEE-2020 Special Issue.The article describes in detail alumina powder synthesis by different methods at varying parameters. The technique of obtaining ceramics and the research of the optical properties for determining the materials with the maximum luminescence efficiency is presented. The concentration of the luminescence intrinsic centers and various defects differ for ceramics synthesized by different methods. It is determined that ceramics based on the powder synthesized by a sol-gel method has the maximum thermoluminescence intensity in the Fcenter peak, whereas for the peak of 360 °C it is obtained with the powder prepared by precipitation of aluminum nitrate with a PEG-20000 stabilizer.This work was financially supported by the Russian Science Foundation, project No. 18-72-10082

Phase Diagram of Pressure-induced Superconductivity and its Relation to Hall Coefficient in Bi2Te3 Single Crystal

Pressure-induced superconductivity and its relation to corresponding Hall coefficient (RH) have been reported for Bi2Te3, one of known topological insulators. A full phase diagram is presented which shows a complex dependence of the superconducting transition temperature as a function of pressure over an extensive range. High-pressure RH measurements reveal a close relation of these complex behaviors, particularly, a dramatic change of dRH/dP before structural phase transition and a pressure-induced crossover on RH in the high pressure phase were observed.Comment: 14 pages and 3 figure

SOL-GEL SYNTHESIS OF Li7-xLa3Zr2-xTaxO12 (x=0.1-0.7) SOLID ELECTROLYTES

Твердые электролиты Li7-xLa3Zr2-xTaxO12 (x=0.1-0.7) были синтезированы с помощью золь-гель метода. Полученные соединения имеют кубическую структуру Ia-3d. В исследуемой системе наибольшей электропроводностью при 25 °C обладает твердый электролит Li6.4La3Zr1.6Ta0.4O12, 1.2·10-4 См/см.Li7-xLa3Zr2-xTaxO12 (x=0.1-0.7) solid electrolytes have been synthesized by solgel method. The obtaining compounds have a cubic structure Ia-3d. The Li6.4La3Zr1.6Ta0.4O12 solid electrolyte has the highest total conductivity, 1.2·10-4 S/cm at 25 °C

ELECTRICAL CONDUCTIVITY OF Li6.75-3xAlxLa3Zr1.75Nb0.25O12 (x=0–0.25) SOLID ELECTROLYTES

В представленной работе с помощью золь-гель метода синтеза получены твердые электролиты Li6.75-3xAlxLa3Zr1.75Nb0.25O12 (x=0–0.25). Изучены их фазовый состав и электропроводность. Согласно данным РФА, полученные твердые электролиты с x>0.10 содержали примесь в виде La2Zr2O7. Показано, что состав Li6.6Al0.05La3Zr1.75Nb0.25O12 имеет наибольшую электропроводность при 25 °C, которая составляет 6.3·10-4 См/см.Li6.75-3xAlxLa3Zr1.75Nb0.25O12 (x=0–0.25) solid electrolytes have been obtained by sol-gel method. Their phase composition and conductivity have been studied. According to XRD analysis the obtained solid electrolytes with x>0.10 have impurity in the form of La2Zr2O7. The Li6.6Al0.05La3Zr1.75Nb0.25O12 solid electrolyte has the highest total conductivity, 6.3·10-4 S/cm at 25 °C.Исследование выполнено при финансовой поддержке гранта Президента РФ № МК-1382.2019.3