Cu Insertion Into the Mo<sub>12</sub> Cluster Compound Cs<sub>2</sub>Mo<sub>12</sub>Se<sub>14</sub>: Synthesis, Crystal and Electronic Structures, and Physical Properties

Mo-based cluster compounds are promising materials for high-temperature thermoelectric applications due to their intrinsic, extremely low thermal conductivity values. In this study, polycrystalline cluster compounds Cs<sub>2</sub>Cu<sub><i>x</i></sub>Mo<sub>12</sub>Se<sub>14</sub> were prepared for a wide range of Cu contents (0 ≤ <i>x</i> ≤ 2). All samples crystallize isostructurally in the trigonal space group <i>R</i>3̅. The position of the Cu atoms in the unit cell was determined by X-ray diffraction on a single-crystalline specimen indicating that these atoms fill the empty space between the Mo–Se clusters. Density functional theory calculations predict a metallic ground state for all compositions, in good agreement with the experimental findings. Magnetization measurements indicate a rapid suppression of the superconducting state that develops in the <i>x</i> = 0.0 sample upon Cu insertion. Transport properties measurements, performed in a wide temperature range (2–630 K) on the two end-member compounds <i>x</i> = 0 and <i>x</i> = 2, revealed a multiband electrical conduction as shown by sign reversal of the thermopower as a function of temperature.