| Summary: | Bi0.925Ca0.075Cu1−xSeO (x = 0–0.10) samples were fabricated by combining a two–step solid–state reaction with spark plasma sintering, and the effect of Cu vacancies on the crystal structure and thermoelectric properties of Bi0.925Ca0.075Cu1−xSeO samples was investigated. Bi0.925Ca0.075Cu1−xSeO formed a single phase with a tetragonal crystal structure (P4/nmm space group). X–ray photoelectron spectroscopy (XPS) analysis revealed that the Cu ions existed as a mixture of Cu1+ and Cu2+ ions and that the Bi ions existed as a mixture of Bi3+ and Bi4+ ions. The relative concentrations of Cu2+ and Bi4+ ions increase with increasing Cu vacancy, which in turn reduce the carrier concentrations. The Cu vacancies enhance the thermoelectric power factor and reduce the lattice thermal conductivity. The largest dimensionless figure–of–merit (0.62) was obtained for Bi0.925Ca0.075Cu0.90SeO at 600 °C. In this work, we optimized the thermoelectric properties of Bi0.925Ca0.075CuSeO by enhancing the power factor and suppressing the thermal conductivity through the formation of Cu vacancies.
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