Thermoelectric power of CuCrxVySe4p-type spinel semiconductors

Structural, electrical and magnetic measurements of polycrystalline CuCrxVySe4 spinels with x=1.79, 1.64 and 1.49 and y=0.08, 0.22 and 0.45, respectively, are presented. The compounds under study crystallize in regular system of a normal spinel type MgAl2O4 structure with the space group symmetry Fd3m. The chromium spins are coupled ferromagnetically and show both strong long- and short-range magnetic interactions evidenced by the large values of the Curie (TC) and Curie–Weiss (θCW) temperatures, decreasing from TC=407 K and θCW=415 K for y=0.08, via TC=349 K and θCW=367 K for y=0.22 to TC=283 K and θCW=293 K for y=0.45, respectively. In all the studied spinels a change of the electrical conductivity character from the semiconductive into the metallic one above 230 K was observed. A detailed thermoelectric power analysis showed a domination of diffusion thermopower component, maximum of phonon drag component at 230 K, a decrease of impurity component with increasing V content, as well as the weak magnon excitations at 40 K.

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► The semiconductive-metallic transition is mainly caused by the carrier diffusion and phonon excitations.
► The grain boundaries and oxidation layers dump the magnon excitations in the studied polycrystals.
► The higher the non-stoichiometry, the higher is the impurity thermopower.