This paper presents the results of model calculations of the structure of the Cu-Te system at low temperatures, as well as the results of a study of the structure and phase transitions of synthesized non-stoichiometric compounds of copper tellurides. For the first time, using the USPEX evolutionary algorithm, model computer calculations of the search for stable phases of copper tellurides Cu n Te m (n,m = 1÷10) were carried out. At temperature T = 0 K and pressure p = 1 atm. As stable structures, the compositions Cu 5 Te 4 , Cu 3 Te 2 , and Cu 7 Te 4 were identified, which are indicated in the triclinic and monoclinic syngonies. Based on the study of the phase diagram, calorimetric measurements and X-ray diffraction studies of experimentally synthesized samples of copper telluride, it was found that the non-stoichiometric compositions Cu 1.96 Te, Cu 1.85 Te, Cu 1.80 Te and Cu 1.75 Te at room temperature are single-phase. The Cu 1.85 Te, Cu 1.80 Te, and Cu 1.75 Te compounds are described by hexagonal crystalline superstructures obtained on the basis of the Novotny phase for Cu 2 Te with different degrees of unit cell parameter multiplicity. Cu1.96Te at room temperature is indicated in an orthorhombic phase with lattice parameters that are also multiples of the unit cell parameters of the Novotny phase. At high temperatures, all compositions of Cu 2−x Te (x=0.04, 0.15, 0.20, 0.25) transform into high-temperature disordered FCC structures that exist up to their melting point. It is shown that in these compounds the transition of a low-temperature hexagonal and orthorhombic structure to a high-temperature FCC phase occurs through a series of polymorphic phase transformations.

This article presents the results of inelastic scattering studies of neutrons and copper and silver chalcogenides at a temperature of 300 K in the non-superionic phase. We were the first to obtain dynamic structural factors and generalized the phonon densities of the states of these compounds. Inelastic peaks observed at energies of 3–5 meV presumably correspond to the acoustic vibrations of phonons. The phonon spectra of copper and silver chalcogenides have features characteristic of compounds that are structurally disordered.

В работе представлены результаты расчета зонной структуры, плотности состояний и распределения электронной плотности в двумерном суперионном проводнике CuCrS2 при температуре 300 К и 673 К в рамках теории функционала электронной плотности с помощью программного пакета Quantum Espresso. Расчеты были проведены для гексагональной структуры (R3m). Исходя из полученных данных, сделан вывод о том, что данные соединения являются полупроводниками, а химическая связь носит преимущественно ковалентный характер. This paper presents the results of calculating the band structure, density of states, and electron density distribution in a two-dimensional superionic conductor CuCrS2 at temperatures of 300 K and 673 K within the framework of the electron density functional theory using the Quantum Espresso software package. The calculations were performed for a hexagonal structure (R3m). Based on the data obtained, it was concluded that these compounds are semiconductors, and the chemical bond is predominantly covalent.

В работе рассмотрена фазовая диаграмма системы Cu-Se, проведены модельные компьютерные расчеты с помощью программы USPEX, уточнены структуры селенидов меди стехиометрических и нестехиометрических составов при различных давлениях. Показано, что при абсолютном нуле температуры и давлении 0.1 GPa стабильными являются составы Cu6Se6 и Cu6Se4, имеющие тригональную структуру. The paper considers the phase diagram of the Cu-Se system, carried out model computer calculations using the USPEX program, and refined the structures of copper selenides of stoichiometric and non-stoichiometric compositions at various pressures. It is shown that, at absolute zero temperature and a pressure of 0.1 GPa, the compositions Cu6Se6 and Cu6Se4, which have a trigonal structure, are stable.

— The electron density distribution in solid solutions between the high-temperature (cubic) phases of copper and silver chalcogenides has been assessed within the density-functional approach using pseudopotential calculations implemented in the Quantum Espresso program package. The results indicate that Cu–Ag cation substitutions and S–Se–Te anion substitutions lead to a reduction in electron shell overlap.

The paper presents the results of model calculations of the phase diagram of the Cu-Te system. A comparative analysis of the experimentally obtained data with theoretical calculations for the obtained model compounds is presented.

For the first time, the results of investigations of ion transport phenomena in high-temperature modifications of single-crystalline copper selenide are presented depending on the temperature and the composition within the homogeneity region as well as the effect of the degree of perfection of single-crystalline samples on the ion transfer. It is found that the activation energy estimated from the temperature dependences of the ionic conductivity for perfect single crystals is significantly higher than in polycrystalline samples and increases with a deviation from stoichiometry. For single crystals, lower values of ionic conductivity are observed. The ionic conductivity in the temperature range of 573–723 K is 1.5–2 times higher for polycrystalline samples than for single crystals.

В работе представлены результаты модельных расчетов фазовой диаграммы системы CuSe. Приведен сравнительный анализ экспериментально полученных данных с теоретическими расчетами для полученных модельных соединений. The paper presents the results of model calculations of the phase diagram of the CuSe system. A comparative analysis of the experimentally obtained data with theoretical calculations for the obtained model compounds is given.

В работе представлены результаты расчета зонной структуры и распределения электронной плотности в AgCuS с помощью программного пакета Quantum Espresso, Указанная структура была рассчитана для высокотемпературной кубической фазы. The band structure of AgCuS has been investigated theoretically using the Quantum Espresso software package. That structure was calculated for the hightemperature cubic phase.

The article presents the results of investigations of copper selenide Cu1.75Se using the NMR method. The 77Se NMR spectrum for Cu1.75Se is a single line with full width at half maximum (FWHM) of 4 kHz at the temperature of 250 K. Within the temperature range of 200–450 K, the rates of transverse and longitudinal relaxation are equal. This phenomenon is mainly typical of a liquid, where the homonuclear dipole-dipole interaction is effectively averaged due to the Brownian motion of molecules. In this case, the main mechanism that averages the dipole-dipole interaction is the motion of copper ions. Below 200 K, copper ions are partially localized due to the phase transition, and the behavior of the spin-spin and spin-lattice relaxation rates (as well as their values) are different.

В работе представлены результаты исследований явлений ионного переноса в высокотемпературных модификациях монокристаллического селенида меди в зависимости от температуры и состава в пределах области гомогенности, а также влияния степени совершенства монокристаллических образцов на ионный перенос. Энергия активации, оцененная из температурных зависимостей ионной проводимости для совершенных монокристаллов значительно выше, чем в поликристаллических образцах и с отклонением от стехиометрии увеличиваются. Для монокристаллов наблюдаются более низкие значения ионной проводимости и химической диффузии. The paper presents the results of studies of the phenomena of ion transfer in high-temperature modifications of singlecrystal copper selenide as a function of temperature and composition within the homogeneity region, as well as the effect of the degree of perfection of single-crystal samples on ion transfer. The activation energy estimated from the temperature dependences of the ionic conductivity for perfect single crystals is significantly higher than in polycrystalline samples and increases with deviation from stoichiometry. Single crystals have lower values of ionic conductivity and chemical diffusion.

Представлены результаты исследований диффузионных явлений в соединениях СuСrS2, АgСrS2 и их сплавах. Определены коэффициенты хаотической диффузии из измерений парциальной ионной проводимости по соотношению Нернста–Эйнштейна для сплавов CuхAg1 - хCrS2. Для всех составов методом радиоактивных изотопов найдены коэффициенты самодиффузии серебра. Для соединения АgСrS2 проведены исследования самодиффузии серебра в интервале температур 473–693 K. Определены величины энергии активации процесса диффузии и значение фактора корреляции. Показано, что экспериментально определенная величина фактора корреляции хорошо согласуется с теоретически рассчитанным значением. Для всех исследуемых составов в интервале температур 473–723 K определены величины коэффициентов химической диффузии. Показано, что высокие по сравнению с коэффициентами хаотической диффузии значения коэффициентов химической диффузии обусловлены высокими значениями термодинамических факторов.

This work presents the results of studies of diffusion phenomena in the compounds of CuCrS2, AgCrS2, and their alloys. Chaotic diffusion coefficients are determined on the basis of measurements of partial ion conductivity using the Nernst–Einstein relationship for the CuxAg1–xCrS2 alloys. For all compositions, the method of radioactive isotopes was used to find self-diffusion coefficients of silver. Studies of silver self-diffusion for the compound of AgCrS2 were carried out in the temperature range of 473–693 K. The values of diffusion activation energy and the correlation factor are determined. It is shown that the experimentally determined value of the correlation factor agrees well with the theoretically calculated value. The values of chemical diffusion coefficients are determined in the temperature range of 473 to 723 K for all the studied compositions. It is shown that the values of chemical diffusion coefficients that are high as compared to the chaotic diffusion coefficients are due to the high values of thermodynamic factors.

The structural peculiarities of CuCrS 2 and AgCrS 2 and the phase ratios in the alloys Cu x Ag 1− x CrS 2 ( x = 0–1) of these compounds were studied at 293–773 K. CuCrS 2 was shown to have unlimited solubility in AgCrS 2 in disordered phases. Ion conductivity was measured for all compositions. At the phase transition point, the activation energy of ion conductivity changed abruptly. The chemical diffusion coefficients and ion transport numbers were determined from the set-in and decay curves of concentration polarization.