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 (Kph). Large anharmonicity in thermodynamically stable (Bi0.67Cr0.33)2Te3 reduces the in-plane room temperature Kph by approximately 79%. However, the latter is found to lie above Cahill's limit (Kmin) of the material which is an indication of the ability to achieve such a significant reduction of Kph. 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.

Automated summary

By studying the impact of magnetism-induced on bismuth telluride in the doped system, it is found that the nonlinearity induced by magnetic moment can effectively reduce the lattice thermal conductivity; the variance of internal energy affects the thermal conductivity, however, the thermal conductivity varies for different configurations at the same doping level.