Design and optimization of high-performance GeTe-based thermoelectric materials

Design and optimization of high-performance GeTe-based thermoelectric materials

Thermoelectric materials can achieve a conversion effect between heat energy and electricity. The conversion efficiency of thermoelectric materials is determined by the dimensionless figure of merit (zT), zT= S2σT/κtot, where S, σ, S2σ, and κtot represent the Seebeck coefficient, electrical conductivity, power factor, and total thermal conductivity, respectively. The pristine GeTe has a high σ due to the high carrier concentration (np) induced by intrinsic Ge vacancies. This high np also led to a low S which obtained a relatively low S2σ. Thus, combined with a relatively high κtot, a peak zT value of ~1 was obtained in GeTe. Rare earth elements doping can affect the transport properties of GeTe thermoelectric materials with below advantages, including aliovalent elements doping to reduce np, the localized magnetic moments due to the unfilled 4f-electrons, the large mass fluctuation, and strain-field fluctuation effect on point defect scattering. All these features motivate us to investigate the rare earth elements doped GeTe system for the purpose of reducing the κlat, exploring the effect of doping with local magnetic moment elements on the thermoelectric properties of GeTe. This project is conducted in the following parts: The thermoelectric performance of GeTe-based thermoelectric materials can be significantly enhanced by substituting REs (Eu, Gd, Er, and Tm) at the Ge site of GeTe. The zTave are increased from 0.38 of pristine GeTe to ~ 0.60 of Ge0.98RE0.02Te at the entire temperature range. Lu was found to have a relatively small radius and electronegativity difference with Ge compared with other rare earth elements, which can induce a high doping level in GeTe. A peak zT of 1.75 at 673 K and an average zT of 0.92 within the temperature range of 303-723 K are obtained in Ge0.9Lu0.02Sb0.08Te. Rare earth Nd doping in the TAGS-85 (GeTe85(AgSbTe2)15) system obtained the highest zT values of 1.65 at 727 K. Overall, several breakthroughs in GeTe thermoelectrics have been made and documented in journal papers. The challenges of high-performance n-type GeTe and the practical application of GeTe thermoelectric devices still need to be further investigated.

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