Effects of Bi doping on thermoelectric properties of La_0.1Sr_0.9TiO₃ ceramics

La_0.1Bi_xSr_0.9-xTiO₃(x=0, 0.05, 0.075, 0.1) ceramics were fabricated at 1 500℃ for 4 h in 5%H₂+95%N₂(V/V) reduction atmosphere. The phase composition, microstructure and thermoelectric properties were investigated. The results indicated that the main phase of the samples doped with Bi was SrTiO₃, and trace Bi₂O₃ was observed when the Bi doping content is more than 0.075. The grain of the samples doped with Bi was fully developed, regularly shaped and combined closely, suggesting the good sintering effect of Bi₂O₃. Moreover, the electric conductivity and the absolute Seebeck coefficient of La_0.1Sr_0.9TiO₃ ceramics increased obviously with the doping of Bi, indicating that the carrier concentration and carrier mobility were greatly improved by the Bi doping. The power factor of the sample with x=0.075 was maximum, which attained 692 μW·m^-1·K^-2at 400℃. Though the thermal conductivity of the samples doped with Bi was higher than that of the sample without Bi, the ZT value of the sample with x=0.075 could still reach 0.172 at 500℃, which was increased by 130% compared with that of the sample without Bi.