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 ((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 (L) correlates with both Gruneisen parameter()and sound velocity (v). This provides us with a simple and powerful predictive tool assessing thermal transport in RE-doped Bi2Te3 compounds.