Electronic transport and thermoelectricity in selenospinel Cu${}_{6-x}$Fe${}_{4+x}$Sn${}_{12}$Se${}_{32}$

Abstract

We report a study of selenospinel Cu${}_{6-x}$Fe${}_{4+x}$Sn${}_{12}$Se${}_{32}$ ($x$ = 0, 1, 2) single crystals, which crystalize in a cubic structure with the $Fd\overline{3}m$ space group, and show typical semiconducting behavior. The large discrepancy between the activation energy for electrical conductivity $E_{\rho }$ (32.3 $\sim$ 69.8 meV), and for thermopower $E_{\text{S}}$ (3.2 $\sim$ 11.5 meV), indicates a polaronic transport mechanism between 350 and 50 K. With decreasing temperature, it evolves into variable-range hopping conduction. Furthermore, the heat capacity shows a hump around 25(5) K and diverges from the Debye $T^3$ law at low temperatures, indicating the observation of structural glassy features in these crystalline solids.

arXiv commentarXiv admin note: text overlap with arXiv:2210.16447

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