Germanium Vacancy Release and Atomic Off-Centering Engineering for Advanced GeTe Thermoelectrics

Germanium telluride (GeTe) is a leading candidate for medium-temperature applications, yet its performance is intrinsically limited by high carrier concentrations arising from the spontaneous formation of Ge vacancies. Conventional strategies for suppressing Ge vacancies to modulate carrier concentration often sacrifice the beneficial phonon scattering centers. Here, we demonstrate that Ge vacancy release and atomic off-centering engineering enable high-performance GeTe thermoelectrics. Specifically, CdTe alloying introduces Ge vacancy clusters and a hierarchical precipitate structure composed of a matrix, secondary phase, and nanoprecipitates. In parallel, the local off-centering of Ge atoms gives rise to intense phonon coupling and pronounced lattice strain. Simultaneously, CdTe/ZnTe alloying causes bandgap widening, band convergence, and impurity bands, thereby raising the effective mass. Consequently, (Ge_0.92Sb_0.02Bi_0.06Te)_0.96(CdTe)_0.04 and (Ge_0.92Sb_0.02Bi_0.06Te)_0.99(ZnTe)_0.01 attain peak dimensionless figure of merit (zT) values of ∼2.2 and ∼2.1 at 723 K, as well as average zT values of ∼1.4 and ∼1.2 over 323-723 K, respectively. Meanwhile, both samples exhibit a Vickers hardness exceeding 235 HV. This work demonstrates a local structural strategy that offers a promising approach for advancing high-performance thermoelectric materials with low thermal conductivity.