Asymmetric phonon-drag effect and thermoelectric performance in PbTe under strain modulation

Abstract

The intricate interplay between electrical and thermal transport in thermoelectric materials has long garnered significant theoretical interest. Despite long-standing theoretical interest in thermoelectric materials, conventional approaches neglect the phonon-drag effect and explicit electron–phonon coupling. Here, using first-principles calculations in combination with the coupled electron–phonon Boltzmann transport equations, we investigated the strain-dependent thermoelectric transport property of PbTe. We find a pronounced asymmetric strain regulation of phonon drag in PbTe. Under tensile strain, band-gap narrowing and low-frequency TO phonon softening significantly enhance the phonon-drag contribution and correct the anomalous Seebeck sign obtained from the no-drag calculation for p-type PbTe. In contrast, the phonon-drag contribution remains weak in the unstrained and mildly compressed cases. Further calculations show that phonon drag can also be enhanced under stronger compression, but with an origin different from that on the tensile side; this enhancement is mainly associated with the Σ valley becoming the valence-band maximum and the modification of near-Fermi-level electron–phonon scattering channels. These results reveal an asymmetric strain response of phonon drag in PbTe, which is crucial for accurately predicting the Seebeck coefficient.