Influence of point defects on the phonon thermal conductivity and phonon density of states of Bi₂Te₃

The influence of point defects on the lattice thermal conductivity and vibrational properties of Bi₂Te₃ were studied by using equilibrium and non-equilibrium molecular-dynamics simulations. Three types of point defects at various concentrations were considered, namely Bi and Te vacancies and Bi anti-sites. It is shown that point defects can result in a reduction of up to 80% of the bulk thermal conductivity. A detailed analysis of the phonon density of states (PDOS) of the studied systems is provided. Element (Bi or Te) and orientation (in-plane or cross-plane) resolved PDOS were calculated. In agreement with experimental observations and other simulations, features in the PDOS were identified with specific atomic and orientation contributions. Systems containing point defects exhibit a broadening of the PDOS peaks as the defect concentration increases, which is due to the disorder induced by the defects. Such disorder leads to a higher phonon scattering and thus to a lower lattice thermal conductivity. Tuning the point defect type and concentrations during growth may, therefore, provide a route for optimizing Bi₂Te₃ based thermoelectric devices. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)