The structure, composition, and thermoelectric properties of cobalt monosilicide obtained by crystallization from a supersaturated solution–melt in tin are studied. A technique for the synthesis and directional solidification of microcrystalline and bulk textured materials in a single technological cycle is developed.
High values of the thermoelectric figure of merit ( ZT = 1.5) in Mg_2Si–Mg_2Sn solid solutions are caused by a low thermal conductivity and a complex band structure, which is optimal at the ratio of solid-solution components of 40% Mg_2Si and 60% Mg_2Sn. However, the presence of magnesium stannide in a high concentration impairs the mechanical properties and chemical stability of the material limiting its application at high temperatures. Magnesium silicide has a higher stability but a lower figure of merit. The figure of merit is much lower in Mg_2Si-rich solid solutions and amounts to ZT ~ 1. The possibility of increasing ZT in the Mg_2Si_0.8Sn_0.2 solid solution with the additional inclusion of Mg_2Ge in small quantities is investigated here. Samples of Mg_2(Si_1 –_ x Ge_ x )_0.8Sn_0.2 ( x < 0.03) solid solution are prepared by hot pressing. The temperature dependences of the coefficients of the thermoelectric power, electrical conductivity, and thermal conductivity are measured in the range of 300–800 K. An increase in the thermoelectric figure of merit to ZT = 1.1 is shown at T = 800 K in the Mg_2Si_0.78Ge_0.02Sn_0.2〈Sb〉 solid solution.
Исследованы термоэлектрические свойства твердого раствора Mg2Ge0.3Sn0.7, легированного Ga и Li. Получены образцы с концентрацией дырок до 5·1020 см-3. Измерены температурные зависимости термоэдс, электропроводности и теплопроводности от комнатной температуры до 800 K. Наблюдается более высокая подвижность свободных носителей на образцах, легированных литием, чем в образцах с галлием. Максимальная безразмерная термоэлектрическая добротность на исследованных образцах составила 0.42 при 700 K. DOI: 10.21883/FTP.2017.08.44785.54
In this work, we study the properties of GeTe -based alloys, doped with bismuth, with partial substitution of lead for germanium: Ge0.86Pb0.1Bi0.04Te. The aim of the study is to explore the possibility of increasing the thermoelectric efficiency of a compound by combining optimal doping and isovalent substitution to improve the electronic properties with a simultaneous decrease of the lattice thermal conductivity. We studied alloy samples prepared in two different research laboratories using similar, but not completely identical procedures. It is shown that the electronic (thermoelectric power and electrical conductivity) properties of the samples of the two groups are in good agreement with each other. The properties of alloys depend on the thermal history of the samples due to the presence at temperatures of 600–800 K of a phase transition from a low-temperature rhombohedral to a high-temperature cubic structural modification. The thermoelectric figure of merit of alloys reaches a maximum value of 1.5 at a temperature of about 750 K.
Nanocomposite thermoelectrics based on Bi_0.45Sb_1.55Te_2.985 solid solution of p -type conductivity are fabricated by the hot pressing of nanopowders of this solid solution with the addition of SiO_2 microparticles. Investigations of the thermoelectric properties show that the thermoelectric power of the nanocomposites increases in a wide temperature range of 80–420 K, while the thermal conductivity considerably decreases at 80–320 K, which, despite a decrease in the electrical conductivity, leads to an increase in the thermoelectric efficiency in the nanostructured material without the SiO_2 addition by almost 50% (at 300 K). When adding SiO_2, the efficiency decreases. The initial thermoelectric fabricated without nanostructuring, in which the maximal thermoelectric figure of merit ZT = 1 at 390 K, is most efficient at temperatures above 350 K.
The possibility of synthesizing layers of the medium-temperature thermoelectric CrSi2 by hot pressing of the initial components (Cr and Si) has been investigated. The phase composition of samples obtained by hot pressing of Cr and Si before and after annealing in the region of their contact boundary has been investigated by X-ray analysis. It is shown that, under certain conditions, low-temperature synthesis of a CrSi2 layer with a thickness of 50 to 300 μm is possible at the interface between Cr and Si. The synthesis occurs at a temperature significantly lower than that given in the phase diagram, which opens up new technological possibilities for obtaining the CrSi2 compound.
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