ICT2014 Abstracts

  Sulfide minerals such as kesterite, digenite, and tetrahedrite have been revealed to have high thermoelectric performance. The minerals have the advantage of environmental acceptability as well as low cost. In the present paper, we report the thermoelectric properties of the synthetic colusites Cu₂₆V₂X₆S₃₂ (X = Ge, Sn) with the cubic primitive structure.

  Polycrystalline samples of Cu₂₆V₂X₆S₃₂ (X = Ge, Sn) have been synthesized by the direct reaction of raw elements at high temperatures in evacuated quartz tubes. Both samples with X = Ge and Sn exhibit metallic electrical resistivity (0.4 mΩcm) and low thermopower (+30 μV/K) at 300 K. The metallic feature and Pauli-paramagnetic behavior are consistent with the electron-deficient character derived from a “nonmagnetic” formula Cu¹⁺₂₆V⁵⁺₂X⁴⁺₆S^2-₃₂. In fact, electron doping by the substitution of Zn for Cu leads to an increase in both electrical resistivity and thermopower. Samples of Cu_26-xZn_xV₂X₆S₃₂ (x = 0 and 2) exhibit rather high power factors of ~0.2 mW/K²m at 300 K. The resistivity of the sample with x = 4 exhibits three-dimensional variable-range-hopping conduction below 50 K, indicating the filling of the unoccupied states in the valence band by the doped electrons. The dependence of the high-temperature thermoelectric properties on the Zn composition will be presented and discussed in comparison with that for Cu_12-xZn_xSb₄S₁₃ tetrahedrite.