Enhanced thermoelectric properties of Sb-doped BiCuSeO due to decreased band gap

Abstract

As the best oxide based thermoelectric materials, the BiCuSeO compounds with very low lattice thermal conductivity and high figure of merit have been widely investigated because of the good thermal/chemical stability, low price and environmental friendliness. In this paper, the Bi1-xSbxCuSeO (x = 0, 0.005, 0.01, 0.02, 0.05, 0.08) oxychalcogenides were prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process in order to improve the thermoelectric properties. The effect of Sb doping on the microstructure and thermoelectric properties of p-type BiCuSeO ceramic has been investigated in detail. To analysis the change rule of the thermoelectric properties of Bi1-xSbxCuSeO due to Sb replacing Bi site, the lattice structure and electronic behavior of BsCuSeO (Bs = Bi or Sb) were calculated and simulated, respectively. The band gap of BsCuSeO has been reduced from 0.478 eV to 0.329 eV, and the bond length of Cu/Bi-Se has been decreased, the hole pocket in the band structure has been deeper, and the peaks of Cu/Se orbitals in the decomposed partial density of states have been broadened after Bi site was replaced by element Sb, which resulted in the significant increase of carrier concentration and electrical conductivity, while still keep a relatively high Seebeck coefficient and low thermal conductivity. The maximum power factor of 0.36 mWm−1K−2 and ZT value of 0.73 were obtained for the Bi0.95Sb0.05CuSeO at 873 K, which was 65% higher than that of the undoped stoichiometry BiCuSeO ceramic.