Band flattening and localized lattice engineering realized high thermoelectric performance in GeTe

Abstract

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 were achieved in the 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, which contributes to the large density-of-states effective mass, resulting in an 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 Ge_0.85Ca_0.05Sb_0.1Te 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 Ge_0.85Ca_0.05Sb_0.1Te sample, leads to the minimum κ_L 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.