On the Influence of Rare Earth Dopants on Thermal Transport in Thermoelectric Bi₂Te₃ Compounds: An Ab Initio Perspective

A density functional theory (DFT) study of thermal transport properties of rare earth (RE) doped Bi₂Te₃ compounds (RE = Y, La, Eu, Gd, and Lu) is reported. The calculations reveal strong nonmonotonous concentration dependence of the lattice thermal conductivity (κ_L) with local minimum in the region of 2–3 at.% dopant concentration for all dopants in the series except Eu. This behavior is associated with the presence of impurity phonon modes in the frequency range of 0–2 THz. The low-frequency parts of the phonon spectra vary substantially for different divalent and trivalent RE dopants, which results in different phonon scattering events for different dopants. The concentration dependence of κ_L correlates with both Grüneisen parameter (γ) and sound velocity (v). This provides us with a simple and powerful predictive tool assessing thermal transport in RE-doped Bi₂Te₃ compounds.