Thermoelectric transport properties in p-type PbTe from first principles*

A high valley degeneracy of electronic bands in a material leads to its large efficiency of conversion between thermal and electrical energy, quantified by the thermoelectric figure of merit (ZT). Large ZT enhancements due to the alignement of the valence band maxima at L and Σ (or “valley convergence”) have been demonstrated in p-type PbTe and related materials [1], by tuning temperature and the doping concentration. However, it is still unclear why this strategy of improving ZT works well since the scattering processes between L and Σ valleys can deteriorate thermoelectric properties. Here, we introduce a first principle method to model electron-phonon scattering mechanisms in p-type PbTe [2]. The calculated room temperature thermoelectric parameters are in very good agreement with available experiments. Our model also allows accounting for the temperature dependence of the electronic band structure in thermoelectric transport calculations, which enables us to quantify the effect of L and Σ valley convergence at ~620 K [3] on the ZT values of p-type PbTe.

[1] Y. Pei et al, Nature 473, 66 (2011)
[2] J. Cao et al, Phys. Rev. B 98, 205202 (2018)
[3] J. D. Querales-Flores et al, Phys. Rev. Mater. 3, 055405 (2019)