Reduction in low-temperature thermal conductivity of Cu₂Se via substitution of Se by Te atoms

We report the structural and thermoelectric properties of the Cu₂Se compound with a systematic substitution of Se by Te atom. The bulk polycrystalline Cu₂Se_1-xTe_x samples for the Te concentrations of x = 0.00, 0.02, 0.04, 0.06, and 0.08 were prepared by the solid-state reaction method. The room-temperature XRD studies revealed that the studied samples possess a monoclinic crystal structure. The oxidation state and electronic structure are confirmed by employing X-ray photoemission spectroscopy (XPS). The hardness of the samples increased systematically with an increase in Te doping concentration. The electrical resistivity of the doped samples was found to be increased in comparison to the pure sample. The Seebeck coefficient was positive throughout the temperature range under investigation, indicating that holes are the majority charge carriers in the studied compounds. The thermal conductivity of the doped samples decreased, which is presumably attributed to the point defect scattering. The systematic evolution of thermoelectric properties via substitution of Se by Te over the range (0.00 ≤ x ≤ 0.08) concludes that the overall thermoelectric power factor (PF) and figure of merit (ZT) decrease with Te substitution compared to the pristine Cu₂Se compound.