Cage-Shaped Mo₉ Chalcogenides: Promising Thermoelectric Materials with Significantly Low Thermal Conductivity

International audienceThermoelectric properties of molybdenum selenides containing Mo9 clusters have been investigated between 300 K and 800 K. AgxMo9Se11 (x = 3.4 and 3.8) have been synthesized by solid-state reaction and spark plasma sintering. X-ray diffraction and scanning electron microscopy reveal high purity and good homogeneity of the samples. The thermoelectric power of the samples is positive over the whole investigated temperature range, indicating that the majority of charge carriers are holes. The Seebeck coefficient increases with temperature, and the temperature coefficient of the resistivity is positive. Significantly low thermal conductivity, comparable to values reported for state-of-the-art thermoelectric materials, is observed in this new system, and this is assumed to be associated with the rattling effect from the Ag filler atoms. It has been demonstrated that the electrical and thermal properties correlate to the Ag concentration. For x = 3.8, a promising dimensionless thermoelectric figure of merit of 0.7 is obtained at 800 K