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.