Tuning the thermoelectric properties by manipulating copper in Cu₂SnSe₃ system

Cu_2+xSnSe₃ (0 ≤ x ≤ 0.08) compounds were synthesized by conventional solid-state reaction followed by spark plasma sintering (SPS) technique. Transport properties of the samples were measured as a function of temperature in the temperature range 323–773 K. As compared to Cu₂SnSe₃ sample, the electrical resistivity (ρ) is increased for the sample with x = 0.04, thereafter a decrease is seen with further increase in copper content. Analysis of electrical resistivity indicates that small poloron hoping model is operative in the entire temperature range for all samples. The positive Seebeck coefficient (S) for the samples in the entire temperature range indicates that the majority charge carriers are holes. The highest figure of merit, ZT (= 0.32) was achieved at 773 K for the sample Cu_2.06SnSe₃ which is about 3 times that of Cu₂SnSe₃ sample. Maximum thermoelectric compatibility factor (˜1.28 V⁻¹) was observed at 673 K for the sample Cu_2.08SnSe₃.