Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution

A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the ball milling using different technological modes. Cold and hot pressing at different conditions and also SPS process were used for consolidation of the powder into a bulk nanostructure and nanocomposites. The main factors allowing slowing-down of the growth of nanograins as a result of recrystallization are the reduction of the temperature and of the duration of the pressing, the increase of the pressure, as well as addition of small value additives (like MoS2, thermally expanded graphite or fullerenes). It was reached the thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of the thermoelectric efficiency in bulk nanocrystalline semiconductors based on BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead to improvement of the thermoelectric figure of merit. The theoretical dependence of the electric and heat conductivities and the thermoelectric power as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite accurately correlates with the experimental data.Comment: 35 pages, 24 figures, 4 tables, 52 reference

The effect of equal-channel angular pressing on microstructure, mechanical properties, and biodegradation behavior of magnesium alloyed with silver and gadolinium

The effect of equal channel angular pressing (ECAP) on the microstructure, texture, mechanical properties, and corrosion resistance of the alloys Mg-6.0%Ag and Mg-10.0%Gd was studied. It was shown that ECAP leads to grain refinement of the alloys down to the average grain size of 2–3 μm and 1–2 μm, respectively. In addition, in both alloys the precipitation of fine particles of phases Mg$_{54}$Ag$_{17}$ and Mg$_{5}$Gd with sizes of ~500–600 and ~400–500 nm and a volume fraction of ~9% and ~8.6%, respectively, was observed. In the case of the alloy Mg-6.0%Ag, despite a significant grain refinement, a drop in the strength characteristics and a nearly twofold increase in ductility (up to ~30%) was found. This behavior is associated with the formation of a sharp inclined basal texture. For alloy Mg-10.0%Gd, both ductility and strength were enhanced, which can be associated with the combined effect of significant grain refinement and an increased probability of prismatic and basal glide. ECAP was also shown to cause a substantial rise of the biodegradation rate of both alloys and an increase in pitting corrosion. The latter effect is attributed to an increase in the dislocation density induced by ECAP and the occurrence of micro-galvanic corrosion at the matrix/particle interfaces

Investigation of the microstructure of the fine-grained YPO4_4:Gd ceramics with xenotime structure after Xe irradiation

The paper reports on the preparation of xenotime-structured ceramics by the Spark Plasma Sintering (SPS) method. Phosphates Y$_{0.95}$Gd$_{0.05}$PO$_4$ (YPO$_4$:Gd) were obtained by the sol-gel method. The synthesized nanopowders are collected in large agglomerates 10-50 mkm in size. Ceramics has a fine-grained microstructure and a high relative density (98.67%). The total time of the SPS process was approximately 18 min. High-density sintered ceramics YPO$_4$:Gd with a xenotime structure were irradiated with Xe$^{+26}$ ions (E = 167 MeV) to fluences of $1\times10^{12}$-$3\times 10^{13}$ cm$^{-2}$. Complete amorphization at maximum fluence was not achieved. As the fluence increases, an insignificant increase in the depth of the amorphous layer is observed. According to the results of grazing incidence XRD (GIXRD), with an increase in fluence from $1\times10^{12}$-$3\times 10^{13}$ cm$^{-2}$, an increase in the volume fraction of the amorphous structure from 20 to 70% is observed. The intensity of XRD peak 200 YPO$_4$:Gd after recovery annealing (700$^\circ$C, 18 h) reached a value of ~80% of the initial intensity I0.Comment: 16 pages, 10 figure

Effect of Thermodeformation Treatment on the Structure and Mechanical Properties of Amorphous Ribbons Based on Zirconium

The structure and mechanical properties of amorphous tapes of an alloy Zr62,5Cu22,5Fe5Al10 was investigated in this work. Samples were obtained by melting on a spinning copper wheel. The changes happening in the structure of tapes after thermodeformation treatment was investigated using the methods of transmission electron microscopy and X-ray structural analysis. Vickers microhardness was measured to investigate the effect of the thermodeformation treatment on the mechanical properties of the tapes.В работе исследовалось металлическое стекло состава Zr62,5Cu22,5Fe5Al10. Образцы получали методом литья на вращающийся медный диск. Методами просвечивающей электронной микроскопии и рентгеноструктурного анализа изучены изменения, происходящие в структуре лент после термодеформационной обработки. Для исследования влияния термодеформационной обработки на механические свойства лент была измерена микротвердость по Виккерсу.Исследование выполнено при финансовой поддержке РФФИ в рамках научного проекта № 19-33-90224

Effect of the valence state of ce ions on the phase stability and mechanical properties of the crystals of ZrO<inf>2</inf>-based solid solutions

© 2017, Pleiades Publishing, Ltd. The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce 3+ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce 3+ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce 3+ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals

ИЗМЕНЕНИЕ СТРУКТУРЫ ПРИКОНТАКТНОЙ ОБЛАСТИ ТЕРМОЭЛЕКТРИЧЕСКИХ МАТЕРИАЛОВ НА ОСНОВЕ ТЕЛЛУРИДА ВИСМУТА ПРИ ПОВЫШЕННЫХ ТЕМПЕРАТУРАХ

Destruction of the thermoelectric material on the basis of bismuth telluride under high temperatures, which prevents the use of these materials for a direct conversion of thermal energy into electrical energy, are revealed. Mechanisms of the occurring process are proposed. It is shown that the industrial technology of spark cutting leads to appearance of the damaged layer, which facilitates the penetration of solder into the volume of the thermoelectric material in subsequent soldering of thermoelements.Выявлены разрушения термоэлектрического материала на основе теллурида висмута под воздействием высоких температур, что препятствует при-менению этих материалов для прямого преобразования тепловой энергии в электрическую. Предложены механизмы про-текающих процессов. Показано, что промышленная технология электроискровой резки материа-ла приводит к возникновению нарушенного слоя, который при последующей пайке термоэлементов способствует проникновению припоя в объем термоэлектрического материала

Теллурид кадмия для высокоэффективных солнечных элементов

Problems of the synthesis of cadmium telluride powders having required purity and grain size distribution for high-efficiency solar cells have been analyzed. A test batch of powders has been synthesized and used for the manufacture and study of thin-film solar cell specimens exhibiting parameters compliant with the best worldwide standards. The phase composition of the powders has been studied using X-ray diffraction. Structural analysis and elemental composition measurements have been carried out using electron microscopy. The effect of free tellurium phase in the powders on the endurance of devices manufactured from the powder has been described. We show that excess tellurium in the film specimens whose atoms are predominantly localized along grain boundaries may cause temporal degradation of the electrical properties of the manufactured solar cells due to changes in the parameters of the crystalline structure of the cadmium telluride phase which are caused in turn by changes in the stoichiometric composition of the material. Structural studies of the film specimens have not revealed differences in the film structure before and after endurance tests. A new cadmium telluride powder process route has been developed, proven and tested taking into account the advantages and drawbacks of the previously used process and experiments confirming the correctness of the technical solutions chosen have been conducted.Рассмотрены проблемы производства порошков теллурида кадмия заданных чистоты и гранулометрического состава, предназначенных для изготовления высокоэффективных солнечных элементов. Получена опытная партия порошков, на основе которых изготовлены и исследованы образцы пленочных солнечных элементов с параметрами на уровне ведущих мировых стандартов. Методом рентгеновской дифрактометрии определен фазовый состав образцов порошков и пленок, методом растровой электронной микроскопии — структурный анализ и измерение элементного состава. Описано влияние наличия фазы свободного теллура в порошках на ресурсные характеристики полученных приборов. Показано, что в пленках избыток теллура, который расположен преимущественно по границам зерен, может приводить со временем к ухудшению электрофизических характеристик солнечных элементов из-за изменения параметров кристаллической структуры фазы теллурида кадмия, вызванного изменением стехиометрического состава. Структурные исследования пленок не выявили в них отличий до и после ресурсных испытаний. Разработана, обоснована и опробована новая технологическая схема получения порошков теллурида кадмия с учетом преимуществ и недостатков используемой ранее технологии, проведены эксперименты, подтверждающие правильность выбранных решений.

ИССЛЕДОВАНИЕ ЭФФЕКТОВ, ИНДУЦИРОВАННЫХ СЛАБЫМ МАГНИТНЫМ ПОЛЕМ В ПОРОШКАХ ЖЕЛЕЗА

The effect of magnetic field treatment on the structure and chemical composition of reduced iron powders has been studied. The methods of transmission electron microscopy, X−ray diffraction and X−ray photoelectron spectroscopy have been used, and corrosion rate has been measured. We show that the processing of powders in an installation having an alternating magnetic field of 0.1 T and a frequency of 21 Hz does not result in any changes to the structure and phase composition. Reduced iron powder particles are spherical; the average diameter is of 2−3 microns, the particles being covered with an amorphous shell. Surface chemical composition studies have shown the shell to be a layer of natural ferric oxide/hydroxide forming in air. A method has been developed for determining the thickness of the oxide shell covering the spherical particles based on the relation of photoelectron lines intensities of the zero−valent and oxidized iron. We show that the shell thickness in magnetic field treated specimens is by 10−20% less than that in untreated powder. Corrosion rate measurements in a corrosive environment have shown that magnetic treatment significantly reduces the oxidation rate of the powders: the more the processing time, the lower the corrosion rate.Проведены исследования влияния обработки в магнитном поле на структуру и химический состав порошков восстановленного железа. Использованы методы просвечивающей электронной микроскопии, рентгеновской дифракции и рентгеновской фотоэлектронной спектроскопии, проведены измерения скорости коррозии. Показано, что обработка порошков в установке переменного магнитного поля при напряженности магнитного поля 0,1 Тл и частоте 21 Гц не привела к каким−либо изменениям в структуре и фазовом составе. Форма частиц порошка восстановленного железа сферическая, средний диаметр составляет 2—3 мкм, частицы покрыты аморфной оболочкой. В результате исследования химического состава поверхности частиц установлено, что оболочка представляет собой слой образовавшегося на воздухе естественного оксида/гидроксида трехвалентного железа. Разработана методика определения толщины оксидной оболочки для сферических частиц по отношению интенсивностей фотоэлектронных линий железа с нулевой валентностью и окисленного железа. Показано, что в образцах, обработанных в магнитном поле, толщина оболочки на 10—20 % меньше, чем в необработанном порошке. Обнаружено, что магнитная обработка существенно уменьшает скорость окисления порошков в агрессивной среде: чем больше время обработки, тем меньше скорость коррозии

編集委員

© 2017, Pleiades Publishing, Ltd. The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce 3+ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce 3+ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce 3+ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals