Enhanced Thermoelectric and Mechanical Properties of BaO-Doped BiCuSeO_δ Ceramics

Layered BiCuSeO_δ ceramics with earth-abundant and non-toxic elements can invariably be prospective thermoelectric (TE) materials attributed to their ultralow thermal conductivity with controllable electrical transport properties. In this study, BaO was used as the dopant of p-type to improve the TE properties of BiCuSeO_δ ceramics prepared through solid-state reactions integrated with the technique of spark plasma sintering. The effects of Ba doping on the thermoelectric and mechanical properties of BiCuSeO_δ ceramics were studied at great length. The result shows that the electrical conductivity was optimized to a value of 241 S cm^–1 for the Bi_0.825Ba_0.175CuSeO_δ sample due to the Ba²⁺-ion substitution on Bi³⁺ sites and the introduction of extra holes. The power factor of the Bi_0.825Ba_0.175CuSeO_δ sample was highly enhanced to 765 μWm^–1 K^–2 at 323 K owing to its notably increased electrical conductivity. Simultaneously, the lattice thermal conductivity of the Bi_0.825Ba_0.175CuSeO_δ sample decreased from 0.64 Wm^–1 K^–1 at 323 K to 0.41 Wm^–1 K^–1 at 873 K, which is ascribed to enhanced phonon scattering through the point defects and a secondary phase. Accordingly, a maximum ZT value of 0.85 was achieved for the Bi_0.825Ba_0.175CuSeO_δ sample at 873 K, which is approximately 3 times higher than that obtained for the undoped BiCuSeO_δ ceramic. The hardness of the BiCuSeO_δ ceramics was measured for the first time by using the nanoindentation method.