Influence of nanostructuring on thermoelectric properties of p-type bulk materials based on (Bi, Sb, Te)

Abstract : This work results from the collaboration between IJL and EDF R&D performed under a CIFRE-ANRT convention, in order to improve the coefficient of performance of thermoelectric heat pumps (THPs). THPs attracted attention of EDF due to its numerous environmental advantages, but the main drawback remains its low performance. The objective of our work was thus to investigate the possibility to enhance the performance of the semiconductors used in the thermoelectric modules of the THPs, by nanostructuration. The research was concentrated on the Sb2-xBixTe3-based solid solutions, the most effective materials for the application sought. The nanostructuration was performed by applying the melt-spinning technique (rapid quenching from a melt on a water-cooled cupper wheel) to the material synthesised beforehand from liquid state in quartz tubes. The means of characterisation (XRD, SEM, TEM, HRTEM) gave the possibility to correlate the structural changes with the variation of the thermal and electrical properties (thermoelectric power, electrical resistivity, Hall effect, thermal conductivity) measured over a wide temperature range (5-460 K). The favourable influence of nanostructuration through the decreasing of thermal conductivity was proved. A high dependence of the thermoelectric efficiency of the studied materials on the concentration of defects and stoichiometry is shown. Doping with Te was investigated as a possibility to control the resulting level of the charge carrier concentration. The idea of creating resonant impurity levels by Sn-doping was shown to be non-conclusive presumably due to the complex band structure of the ternary compounds. Nevertheless, relatively high values of the dimensionless TE figure of merit, close to 1.2, were obtained during this work
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Viktoriia Ohorodniichuk. Influence of nanostructuring on thermoelectric properties of p-type bulk materials based on (Bi, Sb, Te). Other. Université de Lorraine, 2014. English. ⟨NNT : 2014LORR0266⟩. ⟨tel-01751297⟩

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