Band Flattening and Localized Lattice Engineering Realized High Thermoelectric Performance in GeTe

As a lead-free material, GeTe, along with its derivatives, has garnered significant attention as a promising medium-temperature range thermoelectric material, offering a balance between high performance and mechanical stability. Here, a peak ZT value of ~ 2.2 at 773 K and an average ZT of 1.6 ranging from 400 to 823 K was achieved in GeTe system by band flattening and localized lattice engineering. The strategy of Ca-Sb co-doping realized band flattening in c-GeTe and band convergence in r-GeTe is implemented, which contributes to the large density-of-states effective mass, resulting in improved Seebeck coefficient (S) and power factor (PF). The band manipulation strategy assisted in achieving the highest PF of 42.6 μW cm-1 K-2 at 763 K, and an average PF of 32.83 μW cm-1 K-2 was achieved for the Ge0.85Ca0.05Sb0.1Te sample. Simultaneously, with Ca-Sb co-doping, the co-existence of core-shell precipitates, nanorod precipitates, and high-density dislocations, along with the dual atom point defects in the matrix of Ge0.85Ca0.05Sb0.1Te sample, leads to the minimum κL value of 0.61 W m-1 K-1 at 773 K. This novel strategy provides guidelines for the development of thermoelectric materials with competitive thermoelectric and robust mechanical properties.