Constructing Localized Van Der Waals Gaps in Cubic-Phase GeMnTe2 Thermoelectric Material.

Cubic-phase GeMnTe2 shows high potential to replace state-of-the-art rhombohedral GeTe for medium temperature thermoelectric application owing to its lower cost. The high structural symmetry can also suppress phase transition during service and provides a superior platform for further band and microstructural engineering. Through Sb2Te3 alloying and Pb substitution, this study realizes a superior peak figure of merit of ≈1.5 at 773 K and a remarkable average figure of merit of ≈0.96 at 323-823 K. Sb2Te3 alloying successfully generates high-density localized van der Waals (vdW) gaps which are able to scattering low-frequency phonons effectively for reduced lattice conductivity; meanwhile, it also enlarges the valence band degeneracy for enhanced power factor. Pb substitution further reduces the hole concentration to an optimal level. The achievements in this work well reveal the efficacy of construing localized vdW gaps in improving matrix material's thermoelectric performance, thus might shed light on other cubic or pseudo-cubic thermoelectric systems.