Phosphide-based thermoelectrics are a relatively less studied class of compounds, primarily due to the presence of light elements, which result 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) among 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 (μW), transport coefficient (σE0), and material quality factor (B), from which we are able to elucidate that the origin of its high zT can be attributed to the platelike 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 for similar stable phosphides as potentially earth-abundant and nontoxic intermediate-temperature thermoelectric materials.
The authors acknowledge support from A*STAR’s Science and Engineering Research Council, project: A1898b0043 on Accelerating Materials Development for Manufacturing and the PHAROS project on Hybrid Thermoelectrics for Ambient Applications: 1527200018 and 1527200019. The authors also acknowledge Singapore MOE AcRF Tier 2 under Grant Nos. 2018-T2-1-010 and MOE2017-T2-2-069, Singapore A*STAR Pharos Program SERC 1527200022, the National Natural Science Foundation of China (61728401).