High Carrier Mobility and High Figure of Merit in the CuBiSe_2 Alloyed GeTe

摘要

According to the Mott's relation, the figure-of-merit of a thermoelectric material depends on the charge carrier concentration and carrier mobility. This explains the observation that low thermoelectric properties of GeTe-based materials suffer from the degraded carrier mobility, on account of the fluctuation of electronegativity and ionicity of various elements. Here, high-performance CuBiSe2 alloyed GeTe with high carrier mobility due to the small electronegativity difference between Cu and Ge atoms and the weak ionicity of Cu-Te and Bi-Te bonds, is developed. Density functional theory calculations indicate that CuBiSe2 alloying increases the formation energy of Ge vacancies and correspondingly reduces the amount of Ge vacancies, leading to an optimized carrier concentration and a high power factor of approximate to 37.4 mu W cm(-1) K-2 at 723 K. Moreover, CuBiSe2 alloying induces dense point defects and triggers ubiquitous lattice distortions, leading to a reduced lattice thermal conductivity of 0.39 W m(-1) K-1 at 723 K. These synergistic effects result in an optimization of the carrier mobility, the carrier concentration, and the lattice thermal conductivity, which favors an enhanced peak figure-of-merit of approximate to 2.2 at 723 K in (GeTe)(0.94)(CuBiSe2)(0.06). This study provides guidance for the screening of GeTe-based thermoelectric materials with high carrier mobility.