Enhancing thermoelectric performance of GeSb4Te7 single crystals through synergistic band and point defect engineering

Abstract

GeSb₄Te₇, a quasi-two-dimensional semiconductor, exhibits high potential in thermoelectric applications. Herein, efficacious Yb/In co-doping has been realized in the GeSb₄Te₇ single crystals prepared by the slow-cooling method to enhance their thermoelectric properties. DFT calculations demonstrate that the inherently low lattice thermal conductivity of GeSb₄Te₇ is associated with its low phonon group velocities and strong lattice anharmonicity. Yb doping at Ge sites significantly lowers the lattice thermal conductivity, primarily by promoting phonon scattering from point defects. Furthermore, In doping creates an impurity band, leading to a distortion in the density of states (DOS) near the Fermi level and contributing to enhanced Seebeck coefficient. Benefiting from enhanced electrical properties and decreased thermal conductivity, the zT of Yb/In co-doped samples is markedly improved: Ge_0.95Yb_0.02In_0.03Sb₄Te₇ single-crystal sample obtains a record peak zT (0.81) at 673 K and maintains an average zT (0.55) between 323 K and 773 K, signifying a rise of 62% and 83%, respectively, compared with the pristine GeSb₄Te₇. This study proposes a novel strategy to boost the thermoelectric properties of layered-structured GeSb₄Te₇ compounds.