Versatile roles of elemental doping in the optimization of the thermoelectric performance of R-GeTe studied by first principles calculations

Abstract

GeTe-based binary chalcogenides have been proved to be potential thermoelectric materials. Their performance can be greatly enhanced by appropriate doping, which not only optimizes carrier concentration, but also suppresses lattice thermal conduction and in some cases enhances band degeneracy. However, controversy exists in explaining the experimental findings. The major discrepancy lies in the mechanism of carrier optimization by doping. The effect of doping on band structure is also inconsistent. In addition, the origin of the suppressed lattice thermal conductivity by doping is also unclear. Herein, a systematic investigation of the versatile roles of elemental doping in R-GeTe was performed using first-principles calculations. The results indicate that Ge vacancies are the source of intrinsically high carrier concentration in R-GeTe. 8 typical dopants were selected to investigate their effect on the defect formation, band structures and phonon transport properties. Among them, Bi and Sb are effective in suppressing Ge vacancies, which can easily optimize carrier concentration, while Cd, Mg, Mn and Yb can enhance the band degeneracy. Moreover, Bi and Sb are very effective in suppressing the lattice thermal conductivity by lowering down the sound velocity and increasing the lattice anharmonicity. Therefore, the internal mechanism of these dopants to optimize the thermoelectric properties of R-GeTe is clarified by theoretical calculations. Our results provide a robust theoretical guidance on the selection of suitable dopants in R-GeTe, which is conducive to the realization of its excellent thermoelectric performance and accelerating its commercial application.