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

GeSb 4 Te 7 , a quasi-two-dimensional semiconductor, exhibits high potential in thermoelectric applications. Herein, efficacious Yb/In co-doping has been realized in the GeSb 4 Te 7 single crystals prepared by the slow-cooling method to enhance their thermoelectric properties. DFT calculations demonstrate that the inherently low lattice thermal conductivity of GeSb 4 Te 7 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 0.95 Yb 0.02 In 0.03 Sb 4 Te 7 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 GeSb 4 Te 7 . This study proposes a novel strategy to boost the thermoelectric properties of layered-structured GeSb 4 Te 7 compounds. • Growing large-sized GeSb 4 Te 7 -based single crystals via the slow-cooling method. • Clarifying the origin of intrinsically low of GeSb 4 Te 7 for the first time. • Revealing the mechanism of enhanced S and reduced . • Achieving maximal of 0.81 at 673 K for Ge 0.95 Yb 0.02 In 0.03 Sb 4 Te 7 .