Temperature induced band convergence, intervalley scattering and thermoelectric transport in p-type PbTe

TL;DR

This study uses first-principles calculations to analyze how temperature-induced band convergence in p-type PbTe enhances thermoelectric performance, revealing that intervalley scattering has limited impact near the convergence point.

Contribution

It provides a detailed first-principles analysis of temperature-induced band convergence and intervalley scattering effects on thermoelectric properties in p-type PbTe, clarifying their roles.

Findings

Maximum figure of merit occurs near band convergence temperature.

Intervalley scattering does not significantly reduce the figure of merit.

Thermoelectric performance peaks at the band convergence point.

Abstract

Achieving high valley degeneracy (i.e. "band convergence") in a material usually results in considerably enhanced thermoelectric properties. However, it is still unclear why this strategy of designing efficient thermoelectric materials is so successful, since the benefit of increased density of states may be severely degraded by intervalley scattering. Using first-principles calculations, we investigate these effects in $p$-type PbTe, where temperature induces alignment of the $L$ and $\Sigma$ valleys at $\sim$~620~K. We explicitly show that the thermoelectric power factor and figure of merit peak near the band convergence temperature. The figure of merit maximum is larger than those of the individual $L$ and $\Sigma$ valleys. Surprisingly, intervalley scattering does not considerably affect the figure of merit near the band convergence temperature and optimal doping conditions, although it reduces the power factor by almost a factor of 2. Our results suggest that band convergence will significantly increase the figure of merit if intervalley scattering is roughly proportional to the density of states and the lattice thermal conductivity is considerably lower than the electronic thermal conductivity, even if intervalley scattering is strong.