Abstract
An ultrahigh figure of merit ZT value ≈2.4 at 773 K for p-type pseudo-layered Sb(2)Te(3)(GeTe)(17) along the parallel direction is reported by synergistically optimizing its electrical and thermal properties via vacancy engineering. The microstructural origin of thermoelectric property enhancement is studied by spherical aberration corrected transmission electron microscopy and its in situ mode. The results reveal that upon annealing, Ge vacancy gaps in quenched samples tend to migrate and recombine into long-range gaps in order to minimize the elastic and electrostatic energies. The recombination of Ge gaps would lead to an overall reduction of carrier concentration and electrical thermal conductivity. The detailed study of Ge vacancies migration via heat treatment and its effects on thermoelectric performance in pseudo-layered Sb(2)Te(3)(GeTe)(17) materials can provide enlightening clues for future research in a number of thermoelectric materials of similar structures.