Enhancing thermoelectric and mechanical performances in BiCuSeO by increasing bond covalency and nanostructuring

The layered oxyselenide BiCuSeO thermoelectric ceramics are attracting much scientific attention for its excellent thermoelectric properties. Herein, Bi_1-xSb_xCuSe_1-xTe_xO (x = 0, 0.01, 0.02, 0.04, 0.06, 0.08) ceramics have been prepared by ball milling (BM) and resistance pressing sintering (RPS) process. The effects of Sb/Te doping and grain size on the thermoelectric/mechanical properties are investigated systematically. For the former, it can tune the Fermi level and promote the band convergence, decreasing the band gap and concurrently enhancing the carrier concentration; for the latter, it can profoundly modify microstructure into an all-scale hierarchical architecture to scatter phonons with broad range of mean free paths, effectively reducing the lattice thermal conductivity. The results indicates that the substitution of Sb/Te resulted in the significantly increase of electrical conductivity and power factor, and BM effectively reduces the grain size to ~ 387 nm in the sample after sintering, which leads to a decrease in the thermal conductivity and an increase in the electrical conductivity. The maximum power factor of 0.72 m Wm⁻¹ K⁻² and ZT value of 1.19 were obtained for Bi_0.92Sb_0.08CuSe_0.92Te_0.08O with BM time = 16 h at 873 K, which was ~ 2.7 and ~ 2.2 times as that of the pristine BiCuSeO ceramic.