Microstructure design via novel thermodynamic route to enhance the thermoelectric performance of GeTe

Abstract

Defect engineering is the core of thermoelectric study: no thermoelectric material can achieve the best performance without implementing proper defects. Designing the appropriate feature size of defects can promote the trade-off between carrier mobility and lattice thermal conductivity. Taking GeTe as an example, the lattice thermal conductivity is mainly contributed by mid- and long-wavelength heat-carrying phonons, while carrier mean free path is close to point defects. Different from the mainstream strategy of oversaturated precipitation of secondary phases, we propose a novel thermodynamically route to rational design microstructures and enhance the thermoelectric performance of GeTe. Thermodynamically, Zn–Cd co-doping reduces the solubility limit of Zn or Cd in GeTe and promotes the generation of nano and micron scale Zn0.6Cd0.4Te secondary phases, thereby reducing lattice thermal conductivity meanwhile leaving a minimal carrier mobility reduction. The further Sb doping significantly reduces carrier concentration and enhances the density-of-state effective mass, thus improving the Seebeck coefficient. In addition, the formed multiscale microstructures via novel thermodynamic route further restrain the lattice thermal conductivity, leading to a maximum zT of 1.60 at 823 K in Ge0.80Sb0.06Zn0.07Cd0.07Te. This work attest to the efficacy of the rational design of microstructures by novel thermodynamic route toward the high zT in GeTe and other TE materials.