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

TL;DR

This study reveals that the peak thermoelectric performance in AgPbmSbTe2+m is linked to phonon broadening caused by electronic state modifications, as observed through inelastic neutron scattering.

Contribution

It demonstrates the lattice dynamical origin of thermoelectric performance peaks in AgPbmSbTe2+m using inelastic neutron scattering data.

Findings

Broadening of acoustic phonon modes in LAST-18 correlates with optimal thermoelectric properties.

Anomalous phonon broadening is due to scattering from electronic states near the Fermi energy.

Thermal conductivity is minimized while electrical conductivity and Seebeck coefficient are maximized at m=18.

Abstract

Phonon densities of states (DOS) for the high performing thermoelectric material, AgPbmSbTe2+m (LAST-m, m = 16, 18, and 20), were extracted from time-of-flight inelastic neutron scattering measurements. The phonon DOS of LAST-18 differs remarkably from LAST-16 and LAST-20 by exhibiting a dramatic broadening of its acoustic modes that increases on heating. This broadening coincides with a minimum in the thermal conductivity, a maximum in the electrical conductivity and Seebeck coefficient, and a related peak in thermoelectric performance. We argue that the anomalous broadening originates with scattering enhanced by modifications to Te-Ag(Sb) bonds caused by their resonant electronic states falling near the Fermi energy for m = 18.