Abstract—The Cu2 – xSe (0.03 ≤ x ≤ 0.23) powders fabricated by mechanochemical synthesis have been studied by X-ray diffraction. The in situ study has been carried out for the temperature dependences of the lattice parameters, the structures, and the phase compositions of the powders in the temperature range 25–350°C. The powder compositions are shown to differ from the charge compositions and are shifted to lower copper concentrations. The estimation of peak half-widths of the cubic β phase indicates an increase in the structure imperfection after the phase transition from the α phase to the β phase of Cu2 – xSe at ~140°C. It is shown that the superpositions of the subtraction solutions (copper vacancies) and interstitials solutions (copper atoms in interstitial sites), whose proportion is changed as a function of temperature and the deviation from stoichiometry, are in the thermodynamic equilibrium in the copper selenide solid solution at room temperature. The change in the slope of the dependence of the lattice parameter of the powder Cu2 – xSe samples on the composition (0.03 ≤ x ≤ 0.23) in the temperature range 25–350°C enables the suggestion that interstitial copper atom concentration increases with temperature and deviation from stoichiometry.

Abstract —The Cu_2 – _ x Se (0.03 ≤ x ≤ 0.23) powders fabricated by mechanochemical synthesis have been studied by X-ray diffraction. The in situ study has been carried out for the temperature dependences of the lattice parameters, the structures, and the phase compositions of the powders in the temperature range 25–350°C. The powder compositions are shown to differ from the charge compositions and are shifted to lower copper concentrations. The estimation of peak half-widths of the cubic β phase indicates an increase in the structure imperfection after the phase transition from the α phase to the β phase of Cu_2 – _ x Se at ~140°C. It is shown that the superpositions of the subtraction solutions (copper vacancies) and interstitials solutions (copper atoms in interstitial sites), whose proportion is changed as a function of temperature and the deviation from stoichiometry, are in the thermodynamic equilibrium in the copper selenide solid solution at room temperature. The change in the slope of the dependence of the lattice parameter of the powder Cu_2 – _ x Se samples on the composition (0.03 ≤ x ≤ 0.23) in the temperature range 25–350°C enables the suggestion that interstitial copper atom concentration increases with temperature and deviation from stoichiometry.

The influence of competing processes of deformation, return, and recrystallization on the structure and properties of thermoelectric materials extruded at different temperatures is investigated. X-ray diffraction analysis, Harman’s method of measuring thermoelectric properties, and hydrostatic weighing are applied. The nonmonotonic dependence of the texture, electrophysical properties, and density on the extrusion temperature is revealed. In order to achieve the best thermoelectric properties of the material, the optimal extrusion temperature is established to be 400°C.

Получены образцы Cu2Se методом механохимического синтеза и компактирования с помощью искрового плазменного спекания и горячего прессования. Методами рентгеновской дифрактометрии и сканирующей электронной микроскопии были исследованы их структура и фазовый состав до и после термообработки. Показано, как изменяется форма и размеры структурных элементов полученных образцов. Исследовано изменение фазового состава селенида меди в интервале температур 25-500oC in situ. DOI: 10.21883/FTP.2017.07.44638.24

It is necessary to take into account the thermal resistances of structural components located between a material and a heat emitting medium (on the cold side) and between a material and a heat absorbing medium (on the hot side) when simulating thermoelectric cooling devices. A dimensionless mathematical model taking into account the mentioned thermal resistances and describing the cooling and heating capacity, voltage, and coefficient of performance of the devices, depending on current, is proposed in this study. Using this model, the optimal values of the current and thermal resistances on the hot and cold side of the devices can be found for implementation of the maximum cooling capacity mode and other operating conditions.

Copper-selenide (Cu2Se) samples are produced by mechanochemical synthesis and compaction by spark plasma sintering and hot pressing. The structure and phase composition of the samples before and after heat treatment are studied by the X-ray diffraction technique and electron microscopy. The character of changes in the shape and size of structural elements of the samples is shown. Variations in the phase composition of copper selenide in the temperature range from 25 to 500°C are studied in situ.

При моделировании термоэлектрических охлаждающих устройств необходимо учитывать тепловые сопротивления конструкционных элементов, расположенных между материалом и теплоотдающей средой (на холодной стороне) и между материалом и теплопринимающей средой (на горячей стороне устройства). В работе предложена безразмерная математическая модель, описывающая холодо- и теплопроизводительность, напряжение питания и холодильный коэффициент устройств в зависимости от тока с учетом указанных тепловых сопротивлений. С помощью данной модели могут быть найдены оптимальные значения тока и тепловых сопротивлений на горячей и холодной стороне устройства для реализации максимальной холодопроизводительности и других режимов работы. DOI: 10.21883/FTP.2017.07.44636.22

This paper reports an x-ray diffraction, scanning and transmission electron microscopy study of regularities in the formation of defect structures in thermoelectric materials at different stages of plastic flow during equal-channel angular pressing in a three-channel configuration. We show that this deformation setup produces a homogeneous fine-grain structure with a preferential texture in which grain cleavage planes arrange along the extrusion axis. These studies of the structure and properties of thermoelectric materials were used to choose the optimum temperature for equal-channel angular pressing corresponding to lower pre-recrystallization temperatures.