Synthesis, Crystal and Electronic Structures, and Thermoelectric Properties of the Novel Cluster Compound Ag₃In₂Mo₁₅Se₁₉

Abstract

Polycrystalline samples and single crystals of the new compound Ag₃In₂Mo₁₅Se₁₉ were synthesized by solid-state reaction in a sealed molybdenum crucible at 1300 °C. Its crystal structure (space group <i>R</i>3̅<i>c</i>, <i>a</i> = 9.9755(1) Å, <i>c</i> = 57.2943(9) Å, and <i>Z</i> = 6) was determined from single-crystal X-ray diffraction data and constitutes an Ag-filled variant of the In₂Mo₁₅Se₁₉ structure-type containing octahedral Mo₆ and bioctahedral Mo₉ clusters in a 1:1 ratio. The increase of the cationic charge transfer due to the Ag insertion induces a modification of the Mo–Mo distances within the Mo clusters that is discussed with regard to the electronic structure. Transport properties were measured in a broad temperature range (2–1000 K) to assess the thermoelectric potential of this compound. The transport data indicate an electrical conduction dominated by electrons below 25 K and by holes above this temperature. The metallic character of the transport properties in this material is consistent with electronic band structure calculations carried out using the linear muffin-tin orbital (LMTO) method. The complex unit cell, together with the cagelike structure of this material, results in very low thermal conductivity values (0.9 W m^–1 K^–1 at 300 K), leading to a maximum estimated thermoelectric figure of merit (<i>ZT</i>) of 0.45 at 1100 K