Intrinsically Low Lattice Thermal Conductivity and Anisotropic Thermoelectric Performance in In-doped GeSb_2Te_4 Single Crystals

摘要

Layer-structured GeSb_2Te_4 is a promising thermoelectric candidate, while itsanisotropy of thermal and electrical transport properties is still not clear. Inthis study, Ge_(1-x)In_xSb_2Te_4 single crystals are grown by Bridgman method, andtheir anisotropic thermoelectric properties are systematically investigated.Lower electrical conductivity and higher Seebeck coefficient are observed in thec-axis due to the higher effective mass in this direction. Intrinsically low latticethermal conductivity is also observed in the c-axis due to the weak chemicalbonding and the strong lattice anharmonicity proved by density functionaltheory calculation. Indium doping introduces an impurity band in the bandgapof GeSb_2Te_4 and leads to the locally distorted density of states near the Fermilevel, which contributes to enhanced Seebeck coefficient and improved powerfactor. Ultimately, a peak zT value of 1 at 673 K and an average zT value of 0.68within 323-773 K are obtained in Ge_(0.93)In_(0.07)Sb_2Te_4 along the c-axis direction,which are 54% and 79% higher than that of the pristine GeSb_2Te_4 single crystal,respectively. This study clarified the origin of intrinsic low lattice thermal conductivityand anisotropy transport properties in GeSb_2Te_4, and shed light on theperformance optimization of other layered thermoelectric materials.