Enhancing thermoelectric performance in GeTe through Ge enrichment regulation and AgCuTe alloying

Abstract

Germanium telluride (GeTe) exhibits substantial potential as a thermoelectric material well-suited for mid-temperature applications. The presence of a significant amount of off-stoichiometric Ge leads to the formation of Ge precipitates and vacancies, which exert a pronounced influence on the electrical and thermal transport properties of GeTe. In this study, a heat treatment process is initially applied to alleviate Ge enrichment within pristine GeTe, resulting in the achievement of a uniform distribution of Ge precipitates throughout the matrix. Subsequently, we coarsely optimize the carrier concentration through Bi counter-doping, thereby attaining the desired range for optimal performance. Notably, we finely adjust the Ge/Te ratio through AgCuTe alloying, effectively modulating Ge precipitation, reducing lattice thermal conductivity, and enhancing the thermoelectric performance of GeTe. Consequently, the synthesized sample (Ge0.94Bi0.06Te)0.98(AgCuTe)0.02 exhibits a peak ZT value of approximately 2.27 at 773 K, with an average ZT value of approximately 1.38 within the temperature range of 323 to 773 K, making this material as a prominent candidate for medium-temperature thermoelectric applications.