Synthesis, Crystal Structure, and Transport Properties of the Hexagonal Mo Cluster Compound AgRbMoSe.

Mo-based cluster compounds are promising candidates for thermoelectric applications at high temperatures due to their very low lattice thermal conductivity values. Here, we report on a detailed investigation of the crystal structure and transport properties measured in a wide range of temperatures (2-800 K) of polycrystalline AgRbMoSe. Single-crystal X-ray diffraction shows that this compound crystallizes in the hexagonal space group P6/m. The crystal structure is formed by stacked MoSe units leaving channels that are randomly filled by Rb cations, while Ag cations are located between the MoSe units. The high disorder in the unit cell induced by these atoms and their large anisotropic thermal displacement parameters are two key characteristics that lead to very low lattice thermal conductivity as low as 0.6 W m K at 800 K. The combination of semiconducting-like electrical properties and low ability to transport heat leads to a maximum dimensionless thermoelectric figure of merit ZT of 0.4 at 800 K.