Crystal symmetry enables high thermoelectric performance of rhombohedral GeSe(MnCdTe2)x. (September 2022) - Li, Xiang
Abstract: High symmetry favors high power factor by virtue of the balanced Seebeck coefficient and carrier mobility, nonetheless, the role of crystal symmetry in enhancing the material's thermoelectric performance is abstruse. Here, we employ the interplay between crystal symmetry and native point defects towards high zT of IV-VI semiconductor GeSe, which is scarce in thermoelectric study. Pristine orthorhombic GeSe has a low zT ~ 0.05 due to the high formation energy of Ge vacancy and thus the low carrier concentration (~ 10 16 cm −3 ). Alloying GeSe with MnCdTe2 stabilizes higher-symmetry rhombohedral structure at ambient conditions, thereby effectively lowering the formation energy of Ge vacancy and raising the carrier concentration by four orders of magnitude. Meanwhile, compared to orthorhombic GeSe, the rhombohedral Ge1- y Bi y Se(MnCdTe2 ) x own higher valley degeneracy and smaller band effective mass, rendering the decent Seebeck coefficient and larger carrier mobility, respectively. Moreover, the generated multiscale microstructures in rhombohedral Ge0.96 Bi0.04 Se(MnCdTe2 )0.10, including atomic-scale native Ge vacancies and substitution point defects, nanoscale domain structures, and micron-sized secondary phases effectively depress the lattice thermal conductivity. As a result, a state-of-the-art zT ~ 1.0 at 723 K is achieved in Ge0.96 Bi0.04 Se(MnCdTe2 )0.10 . These results attest to the efficacy of the interplay between crystal symmetry and native point defects towards high performance GeSe-based and other thermoelectric materials. Graphical Abstract: ga1 Highlights: Synergy of crystal symmetry and native point defect enables high figure of merit zT. MnCdTe2 alloying stabilizes rhombohedral GeSe and optimizes carrier concentration. Crystal symmetry regulates band structure and thereby increases the power factor. The induced multiscale microstructures restrain the lattice thermal conductivity. A state-of-the-art zT value of ~ 1.0 at 723 K is achieved.