Low-temperature thermoelectric properties of Pb doped Cu₂SnSe₃

A series of Cu₂Sn_1-xPb_xSe₃ (0 ≤ x ≤ 0.04) compounds was prepared by solid state synthesis technique. The electrical resistivity (ρ) decreased with increase in Pb content up to x = 0.01, thereafter it increased with further increase in x (till x = 0.03). However, the lowest value of electrical resistivity is observed for Cu₂Sn_0.96Pb_0.04Se₃. Analysis of electrical resistivity of all the samples suggests that small poloron hoping model is operative in the high temperature regime while variable range hopping is effective in the low temperature regime. The positive Seebeck coefficient (S) for pristine and doped samples in the entire temperature range indicates that the majority charge carriers are holes. The electronic thermal conductivity (κ_e) of the Cu₂Sn_1-xPb_xSe₃ compounds was estimated by the Wiedemann-Franz law and found that the contribution from κ_e is less than 1% of the total thermal conductivity (κ). The highest ZT ~ 0.013 was achieved at 400 K for the sample Cu₂Sn_0.98Pb_0.02Se₃, about 30% enhancement as compared to the pristine sample.