Prediction of Bi₂Te₃-Sb₂Te₃ Interfacial Conductance and Superlattice Thermal Conductivity Using Molecular Dynamics...

Bismuth telluride (Bi₂Te₃) and its alloys with antimony telluride (Sb₂Te₃) have long been considered to be the best room-temperature bulk thermoelectric (TE) materials. In recent decades, proof-of-concept demonstrations on Bi₂Te₃-Sb₂Te₃ nanostructures have shown high TE performance due to reduction in lattice thermal conductivities. Particularly, ultra-low thermal conductivities have been observed in Bi₂Te₃-Sb₂Te₃ 1D superlattices, leading to thermoelectric figures of merit (ZT) as high as 2.4. In contrast, very few computational studies have been performed to provide insight into the phonon transport across these nanostructures. In this work, we use non-equilibrium molecular dynamics simulations with previously developed force fields to simulate thermal transport across Bi₂Te₃-Sb₂Te₃ interfaces and superlattices. We first calculate the thermal conductance associated with a Bi₂Te₃-Sb₂Te₃ interface across a temperature range of 200-400 K. The values are also compared with thermal conductances calculated by a modified Landauer transport formalism using phonon transmission coefficients obtained from the diffuse mismatch model. Our results show that inelastic scattering processes contribute to an increase in interfacial thermal conductance at higher temperatures. Finally, we calculate the thermal conductivities of Bi₂Te₃-Sb₂Te₃ superlattices with varying period lengths from 2 to 18 nm. A minimum thermal conductivity of 0.27 W/mK is observed at a period length of 4 nm, which is attributed to the competition between incoherent and coherent phonon transport regimes. In comparison with previous experimental measurements in the literature, our results show good agreement with respect to the range of thermal conductivity values and the period length corresponding to the minimum superlattice thermal conductivity.