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.