Intrinsically Low Lattice Thermal Conductivity and Anisotropic Thermoelectric Performance in In-doped GeSb2Te4 Single Crystals

Layer-structured GeSb2Te4 is a promising thermoelectric candidate, while its anisotropy of thermal and electrical transport properties is still not clear. In this study, Ge1-xInxSb2Te4 single crystals are grown by Bridgman method, and their anisotropic thermoelectric properties are systematically investigated. Lower electrical conductivity and higher Seebeck coefficient are observed in the c-axis due to the higher effective mass in this direction. Intrinsically low lattice thermal conductivity is also observed in the c-axis due to the weak chemical bonding and the strong lattice anharmonicity proved by density functional theory calculation. Indium doping introduces an impurity band in the bandgap of GeSb2Te4 and leads to the locally distorted density of states near the Fermi level, which contributes to enhanced Seebeck coefficient and improved power factor. Ultimately, a peak zT value of 1 at 673 K and an average zT value of 0.68 within 323-773 K are obtained in Ge0.93In0.07Sb2Te4 along the c-axis direction, which are 54% and 79% higher than that of the pristine GeSb2Te4 single crystal, respectively. This work clarified the origin of intrinsic low lattice thermal conductivity and anisotropy transport properties in GeSb2Te4, and shed light on the performance optimization of other layered thermoelectric materials.

Automated summary

In this study, Ge1-xInxSb2Te4 single crystals were grown by Bridgman method and their anisotropic thermoelectric properties were systematically investigated. Lower electrical conductivity and higher Seebeck coefficient were observed in the c-axis direction due to the higher effective mass in this direction. Indium doping introduced an impurity band and locally distorted density of states near the Fermi level, contributing to enhanced Seebeck coefficient and improved power factor. Ultimately, Ge0.93In0.07Sb2Te4 exhibited a peak zT value of 1 at 673 K and an average zT value of 0.68 within 323-773 K, which were 54% and 79% higher than that of the pristine GeSb2Te4 single crystal, respectively. This study clarified the origin of intrinsic low lattice thermal conductivity and anisotropic transport properties in GeSb2Te4, and provided insights for optimizing the performance of other layered thermoelectric materials.