Generation of multi-dimensional defect structures for synergetic engineering of hole and phonon transports: enhanced thermoelectric performance in Sb and Cu co-doped GeTe

A facile compositional tuning by Sb and Cu addition is performed to generate engineered defects in GeTe alloys with ultra-low thermal conductivity. Substitution of Sb and Cu at the Ge-site enhances the power factor due to the optimization of carrier concentration while maintaining the convergence of the valence bands. Furthermore, complex multi-dimensional defect structures including 0D (0-dimensional) substituted SbGe and CuGe, 2D twin and inversion boundaries, 3D herringbone structures, 3D embedded nanostructures, and 3D Cu-rich coherent precipitates are generated, which significantly reduce the lattice thermal conductivity benefitting from a collective phonon scattering. Due to this simultaneous manipulation of electronic and thermal transport properties, a maximum thermoelectric figure of merit (zT) of 1.4 was obtained at 723 K.