Evaluation of SrTi _1-xCo _xO ₃ perovskites (0 ≤ × ≤ 0.2) as interconnect materials for solid oxide fuel cells

The compatibility of SrTi _1-xCo _xO ₃ perovskites (0 ≤ × ≤ 0.2) was evaluated for use as interconnect materials in solid oxide fuel cells (SOFCs). Although SrTi _1-xCo _xO ₃ perovskites have a single perovskite phase in the range of 0 ≤ × ≤ 0.2, it was observed for SrTi _0.8Co _0.2O ₃ that Co element agglomerated at the grain boundary during sintering. The dense SrTi _0.8Co _0.2O ₃ sample was destroyed and included Sr ₂TiO ₄ as a secondary phase after reducing treatment at 1000°C. As a result of Co doping, the linear thermal expansion coefficient (TEC) increased remarkably with increasing Co content, but the TEC of SrTi _0.9Co _0.1O ₃ was comparable with those of SOFC cathodes and anodes. Co doping of SrTiO ₃ effectively increased electrical conductivity in air, whereas the conductivity of Co-doped SrTiO ₃ in a reducing atmosphere was much lower than that in air. This suggests that the Co ions ^3+/4+ in the perovskites were earlier reduced into Co ²⁺ ions, compared to Ti ⁴⁺ ions.