Enhanced Thermoelectric and Mechanical Properties of BaO-Doped BiCuSeO_δ Ceramics

Layered BiCuSeOδ 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 BiCuSeOδ 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 BiCuSeOδ 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 Bi0.825Ba0.175CuSeOδ sample due to the Ba2+-ion substitution on Bi3+ sites and the introduction of extra holes. The power factor of the Bi0.825Ba0.175CuSeOδ 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 Bi0.825Ba0.175CuSeOδ 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 Bi0.825Ba0.175CuSeOδ sample at 873 K, which is approximately 3 times higher than that obtained for the undoped BiCuSeOδ ceramic. The hardness of the BiCuSeOδ ceramics was measured for the first time by using the nanoindentation method.