Effect of reducing annealing on the microstructure and thermoelectric properties of La–Bi co-doped SrTiO₃ ceramics

Sr_1−xLa_xTiO₃ (SLTB) ceramics were fabricated by conventional solid state reaction method. SLTB ceramics were sintered in air, argon and nitrogen atmospheres and then annealed in argon and graphite (Ar + C) atmosphere. The effect of reducing annealing atmosphere on the microstructure and thermoelectric properties of La–Bi co-doped SrTiO₃ ceramics was investigated. The results showed that the S_0.9L_0.1TB ceramics sintered in argon have the lowest resistivity (5.6 × 10⁴ Ω cm). And the resistivity of S_0.9L_0.1TB ceramics annealed in Ar + C environment at 1450 °C for 16 h decreased significantly (6–7 orders of magnitude). The Seebeck coefficient is negative with the increasing absolute value at elevated temperature. The thermal conductivity decreased with the temperature increased. The power factor and electrical conductivity increase first and then decrease with increasing temperatures. S_0.9L_0.1TB ceramics have a maximum value of Seebeck coefficient (−255 μV/K) at 1073 K and the figure of merit ZT_1073K = 0.269.