Thermoelectric Properties of Ternary and Quaternary Mo6 and Mo9 Cluster Selenides

Abstract

Mo-based cluster compounds containing Mo6 and Mo9 cluster units have long been known for their rich chemistry and the diversity and complexity of their crystal structures. While most studies have mainly focused on their crystallographic properties, recent investigations have pointed out their potential for thermoelectric applications in power generation. These compounds derive their good properties from the three-dimensional arrangement of the clusters between which cations reside. This inherent disorder strongly limits the ability of these materials to transport heat that often leads to a temperature dependence of the lattice thermal conductivity that mirrors that observed in glassy systems. In addition, most of these compounds can be driven from a metallic toward a semiconducting state through insertion of additional cations. Here, we review the recent progress made on determining the transport properties of these compounds, discussing in particular the key ingredients that lead to their peculiar thermal properties, and examine possible future directions to further enhance their thermoelectric properties.