Tuning the Lattice Thermal Conductivity in Bismuth Telluride via Cr Alloying
Decreasing the thermal conductivity of a thermoelectric material is always a prerequisite for its potential application. Using first-principle calculations, we examine the magnetism-induced change in lattice thermal transport in bismuth telluride. The source of magnetic moment, Cr in the doped system, weakly magnetizes the coordinated Te atoms to make the latter’s phonon softer than that in the pure compound. Although the transition metal dopants do not participate directly in the heat conduction process, the anharmonicity induced by them favors reducing the lattice thermal conductivity (κph). Large anharmonicity in thermodynamically stable (Bi0.67Cr0.33)2Te3 reduces the in-plane room temperature κph by approximately 79%. However, the latter is found to lie above Cahill’s limit (κmin) of the material which is an indication of the ability to achieve such a significant reduction of κph. The thermal conductivity, strictly, does not vary monotonically with doping concentration. For any particular doping level, the thermal conductivity is different for different configurations which is related to the internal energy of the system. We find that the internal energy variance of 0.03 eV would reduce the in-plane thermal conductivity of the room temperature lattice by at least 60% for 50% doping.