Effect of NaF Doping on the Microstructure and Thermoelectric Performance of BiCuSeO Ceramics

The layered oxyselenide BiCuSeO has attracted significant attention due to its ability to demonstrate low thermal conductivity and a high Seebeck coefficient. This research project involved the synthesis of Bi1−xNaxCuSeO1−xFx (x = 0, 0.05, 0.10, 0.15, and 0.20) ceramics using high-energy ball milling and cold isostatic pressing techniques. A comprehensive investigation was conducted to examine the influence of co−doping NaF on the thermoelectric properties of BiCuSeO ceramics. The substitution of Bi3+ with Na+ introduces a substantial number of holes, resulting in a remarkable improvement in the electrical conductivity and power factor. The conductivity was significantly increased from 9.10 S cm−1 (BiCuSeO) to 94.5 S cm−1 (Bi0.85Na0.15CuSeO0.85F0.15) at 323 K. Additionally, at 823 K, the power factor of the Bi0.85Na0.15CuSeO0.85F0.15 sample reached 44.8 × 10−5 W/m K2. Furthermore, the Bi1−xNaxCuSeO1−xFx ceramics demonstrated a minimum thermal conductivity of 0.43 W m−1 K−1. Consequently, the Bi0.85Na0.15CuSeO0.85F0.15 sample achieved a maximum ZT value of 0.78, which is 7.09 times higher than that of the pure BiCuSeO sample (0.11).