Origin of High Thermoelectric Performance in Earth-abundant Phosphide-Tetrahedrite

Phosphide based thermoelectrics are a relatively less-studied class of compounds, primarily due to the presence of light elements which results in high thermal conductivity and inherent stability problems. In this work, we present a stable phosphide-tetrahedrite, Ag6Ge10P12¬ which possesses the highest zT (~0.7) amongst all known phosphides at intermediate temperatures (750 K). We examine the intrinsic electronic and thermal transport properties of this compound by expressing the transport properties in terms of weighted-mobility (μ_W), transport coefficient (σ_(E_0 )) and material quality factor (B), from which we are able to elucidate that the origin to its high zT can be attributed to plate-like Fermi surface and high level of band multiplicity related to its complex band structure. Finally, we discuss the origin of the low lattice thermal conductivity observed in this compound using experimental sound velocity, elastic properties and Debye-Callaway model, thus laying the foundation of similar stable p...