New Metavalent Materials and Why Their Thermal Conductivity is Low

Metavalent materials have recently been introduced as a new class of materials with small bandgap, large Grueneisen parameters, polarizability and Born effective charges. Up to now more than a dozen such materials have been identified. They are typically IV-VI materials with rocksalt structure, and have good thermoelectric and phase change properties. In this talk, we present our characterization of metavalency in some new candidate materials such as LaP, and explain why it has lower thermal conductivity than LaBi despite having lighter mass and higher phonon group velocities. To identify new metavalent materials, we have investigated the effect of physical and chemical pressure (or alloying) on metavalency. In partcular, we looked at the doping of cubic GeTe by In, Bi, Pb and Sb. Such strategies may allow us finding new metavalents and possibly low-thermal conductivity materials for thermoelectric and thermal management applications.