First-Principles Theory of Competing Order Types, Phase Separation, and Phonon Scattering in Thermoelectric Pb-Sb-Ag-Te Alloys

TL;DR

This study uses first-principles calculations to analyze the phase diagram, structure, and phonon properties of Pb-Ag-Sb-Te thermoelectric alloys, revealing nanoscale inhomogeneities that improve performance.

Contribution

It provides a detailed first-principles understanding of phase stability, nanoscale inhomogeneities, and phonon spectra in Pb-Ag-Sb-Te thermoelectric alloys, highlighting their impact on thermoelectric efficiency.

Findings

Nanoscale inhomogeneities are coherent precipitates of ordered phases.

High solubility of PbTe in AgSbTe2; low in the opposite direction.

Differences in phonon spectra enhance thermoelectric performance.

Abstract

Using a first-principles cluster expansion, we shed light on the solid-state phase diagram and structure of the recently discovered high-performance thermoelectrics, Pb-Ag-Sb-Te alloys. The observed nanoscale inhomogeneities are shown to be coherent precipitates of ordered (Ag)m(Sb)n(Te)m+n phases, such as AgSbTe2, all immiscible with rocksalt PbTe. The solubility is high for PbTe in AgSbTe2 and low for (Ag,Sb)Te in PbTe (8% vs. 0.6% at 850 K). The differences in the phonon spectra of PbTe and AgSbTe2 confirm that the inhomogeneities enhance the thermoelectric performance.