Modeling heat transfer in Bi₂Te₃-Sb₂Te₃ nanostructures

Bi₂Te₃-Sb₂Te₃ nanostructures are gaining importance for use in thermoelectric applications following the finding that the Bi₂Te₃-Sb₂Te₃ superlattice exhibits a figure of merit, ZT = 2.4, which is higher than conventional thermoelectric materials. In this paper, thermal transport in the cross-plane direction for Bi₂Te₃-Sb₂Te₃ nanostructures is simulated using the Boltzmann transport equation (BTE) for phonon intensity. The phonon group velocity, specific heat, and relaxation time are calculated based on phonon dispersion model. The interfaces are modeled using a combination of diffuse mismatch model (DMM), and the elastic acoustic mismatch model (AMM). The thermal conductivity for the Bi₂Te₃-Sb₂Te₃ superlattice is compared with the experimental data, and the best match is obtained for specularity parameter, p, of 0.9. The present model is extended to solve for thermal transport in 2-D nanowire composite in which Sb₂Te₃ wires are embedded in a host material of Bi₂Te₃. Unlike in bulk composites, the results show a strong dependence of thermal conductivity, temperature, and heat flux on the wire size, wire atomic percentage, and interface specularity parameter. The thermal conductivity of the nanowire is found to be in the range of 0.034-0.74 depending on the atomic percentage and the value of p.