Thermally insulative thermoelectric argyrodites

Abstract: Ag/Cu-based argyrodites have recently received extensive attention as promising thermoelectric materials. This can be largely understood by the hierarchical chemical bonding structure that allows the existence of high-concentration and highly mobile Ag+/Cu+ ions distributed in the rigid polyanionic framework, since the diffusive cations enable an effective phonon scattering for phononically insulating as that in woods while the rigid framework ensures an electronic charge transport as that in trivial thermoelectric semiconductors. This review focused firstly on the synthesis of both single-crystalline and poly-crystalline argyrodites as well as the chemical compositions, phases and crystallographic features; secondly on the origins of the low lattice thermal conductivity including crystal structure complexity, weak bonded ions, strong lattice anharmonicity and low sound velocity; and thirdly on the electronic band structure characteristics including effective mass and band degeneracy for an evaluation on the electronic transport properties, as well as performance stability. These together lead a perspective on future development of thermoelectric argyrodites to emphasize the enhancement of electronic performance such as by carrier concentration and by manipulating the electronic band structure.