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Abstract Layer‐structured GeSb 2 Te 4 is a promising thermoelectric candidate, while its anisotropy of thermal and electrical transport properties is still not clear. In this study, Ge 1– x In x Sb 2 Te 4 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 GeSb 2 Te 4 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 Ge 0.93 In 0.07 Sb 2 Te 4 along the c ‐axis direction, which are 54% and 79% higher than that of the pristine GeSb 2 Te 4 single crystal, respectively. This study clarified the origin of intrinsic low lattice thermal conductivity and anisotropy transport properties in GeSb 2 Te 4 , and shed light on the performance optimization of other layered thermoelectric materials.
Chen et al. (Tue,) studied this question.