Synthesis, crystal structure, and transport properties of Cu_2.2Zn_0.8SnSe_4-xTe_x (0.1 ≤ x ≤ 0.4)

Quaternary chalcogenides, particular compounds with the stannite structure-type, are of interest for thermoelectrics applications however tellurium-containing compositions have not been extensively investigated. We report on the synthesis and high temperature thermoelectric properties of p-type stannites Cu_2.2Zn_0.8SnSe_4-xTe_x (x = 0.1, 0.2, 0.3, and 0.4). The compositions for each specimen were confirmed with a combination of Rietveld refinement and elemental analysis. Hall measurements indicate that holes are the dominant charge carriers in these materials. The electrical resistivity shows little temperature dependence up to 500 K and then increases with increasing temperature. The thermal conductivity decreases with increasing temperature with no indication of increase at higher temperatures suggesting a minimal bipolar diffusion effect in the thermal conductivity although these materials possess relatively small band-gaps as compared to that of other stannite compositions. A maximum ZT value of 0.56 was obtained at 700 K for Cu_2.2Zn_0.8SnSe_3.7Te_0.3 due to a relatively high Seebeck coefficient and low thermal conductivity.