Lattice thermal transport in group II-alloyed PbTe

TL;DR

This study uses advanced computational methods to analyze phonon scattering mechanisms in alloyed PbTe, revealing how different alloying elements affect lattice thermal conductivity and thermoelectric performance.

Contribution

It applies a DFT-based CSLD approach to model heat transport in PbTe alloys, providing fundamental insights into phonon scattering mechanisms and strain effects.

Findings

CaTe, SrTe, BaTe have higher thermal conductivity than PbTe.

MgTe shows anomalously low thermal conductivity.

Strain and mass disorder significantly reduce phonon lifetimes in alloys.

Abstract

PbTe, one of the most promising thermoelectric materials, has recently demonstrated thermoelectric figure of merit ($ZT$) of above 2.0 when alloyed with group II elements. The improvements are due mainly to significant reduction of lattice thermal conductivity ($\kappa_{l}$), which was in turn attributed to nanoparticle precipitates. However, a fundamental understanding of various phonon scattering mechanisms within the bulk alloy is still lacking. In this work, we apply the newly-developed density-functional-theory (DFT)-based compressive sensing lattice dynamics (CSLD) approach to model lattice heat transport in PbTe, MTe, and Pb$_{0.94}$M$_{0.06}$Te (M=Mg, Ca, Sr and Ba), compare our results with experimental measurements, with focus on strain effect and mass disorder scattering. We find that (1) CaTe, SrTe and BaTe in the rock-salt structure exhibit much higher $\kappa_{l}$ than PbTe, while MgTe in the same structure shows anomalously low $\kappa_{l}$; (2) lattice heat transport of PbTe is extremely sensitive to static strain induced by alloying atoms in solid solution form; (3) mass disorder scattering plays a major role in reducing $\kappa_{l}$ for Mg/Ca/Sr-alloyed PbTe through strongly suppressing the lifetimes of intermediate- and high-frequency phonons, while for Ba-alloyed PbTe, precipitated nanoparticles are also important.