Enhanced thermoelectric performance in BiCuSeO oxyselenides via Ba/Te dual-site substitution and 3D modulation doping

Here, Bi1-xBaxCuSe1-xTexO (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Ba/Te doping on the thermoelectric properties have been investigated systematically. For Ba doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration; for the Te doping based on Ba doping, it can profoundly reduce the difference of electronegativity in (Cu2Se2)(2-) layer, increase bond covalency, and then increase the electrical conductivity. The results indicate that the substitution of Ba/Te resulted in significant increases of electrical conductivity and power factor. Based on this, modulation doping leads to the simultaneous increase of the electrical conductivity and Seebeck coefficient. Finally, the maximum power factor of 0.98 mW m(-1) K-2 and ZT value of 1.17 were obtained for the modulation doped Bi0.90Ba0.10CuSe0.90Te0.10O bulk, which were similar to 3.5 and similar to 2.2 times respectively as those of the pristine BiCuSeO ceramic.