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

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.

submitted to PRL

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• Lattice dynamical origin of peak thermoelectric performance in AgPbmSbTe2+m observed by inelastic neutron scattering