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

Abstract

A density functional theory (DFT) study of thermal transport properties of rare earth (RE) doped Bi 2 Te 3 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 Bi 2 Te 3 compounds.

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“…In this work, we used the values θ = 71 K and γ = 1.2 for all compounds. 30,44 The point defect scattering term, in turn, has the form:…”