Largely Enhanced Seebeck Coefficient and Thermoelectric Performance by the Distortion of Electronic Density of States in GeSbTe.

As one of the state-of-the-art phase-change materials, the stable GeSbTe hexagonal compound also exhibits decent thermoelectric performance with high electrical conductivity and low thermal conductivity. Nonetheless, the excessively high carrier concentration and low Seebeck coefficient are the bottlenecks to achieve high values. In this work, with the intention to optimize the electrical properties, indium was introduced as a potentially donor-like dopant in a series of GeInSbTe samples. The substitution of indium for germanium lowers the density of hole carriers and enhances the Seebeck coefficient. Noticeably, the room-temperature Seebeck coefficient of the doped samples can be three times as large as that of the pristine one, which obviously departures from the theoretically predicted Pisarenko relation based on the single parabolic band model. By virtue of DFT calculations and modeling, the remarkable enhancement of Seebeck coefficient was attributed to the doping-induced local distortion in the electronic density of states. Further insight reveals that indium doping amplifies the bonding character of Ge-Te adjacent to indium and enhances the atomic interaction along the -axis. Due to the optimized electrical properties as well as the suppressed thermal conductivity, a maximal value of 0.78 was achieved in GeInSbTe at 700 K, which is about 40% higher than that of the pristine sample.