Versatile Vanadium Doping Induces High Thermoelectric Performance in GeTe via Band Alignment and Structural Modulation
Qiang Sun, Meng Li, Xiao‐Lei Shi, Shengduo Xu, Wei‐Di Liu, Min Hong, Wanyu Lyu, Yu Yin, Matthew S. Dargusch, Jin Zou, Zhi‐Gang Chen
Abstract
Abstract Owing to the moderate energy offset between light and heavy band edges of the rock‐salt structured GeTe, its figure‐of‐merit ( ZT ) can be enhanced by the rational manipulation of electronic band structures. In this study, density functional theory calculations are implemented to predict that V is an effective dopant for GeTe to enlarge the bandgap and converge the energy offset, which suppresses the bipolar conduction and increases the effective mass. Experimentally, V‐doped Ge 1− x V x Te samples are demonstrated to have an enhanced Seebeck coefficient from ≈ 163 to ≈ 191 µ V K −1 . Extra alloying with Bi in Ge 1− x − y V x Bi y Te can optimize the carrier concentration to further enhance the Seebeck coefficient up to ≈ 252 µ V K −1 , plus an outstanding power factor of ≈ 43 µ W cm −1 K −2 . Comprehensive structural characterization results also verify the refinement of grain size by V‐doping, associated with highly dense grain boundaries, stacking faults, nanoprecipitates, and point defects, reinforcing the wide‐frequency phonon scattering and in turn, securing an ultralow thermal conductivity of ≈ 0.59 W m −1 K −1 . As a result, the Ge 0.9 V 0.02 Bi 0.08 Te sample shows a peak ZT of > 2.1 at 773 K, with an average plateaued average ZT of > 2.0 from 623 and 773 K, which extends better thermoelectric behavior for GeTe over a wider temperature range. This study clarifies the multiple benefits of V‐doping in GeTe‐based derivatives and provides a framework for a new‐type of high‐performance middle‐temperature thermoelectric material.