Fig.3 a plots the electrical conductivity of the BCTCo perovskite oxide against temperature measured in the air and hydrogen atmospheres, in which the conductivity of the BCTb perovskite is also displayed for comparison. As can be seen, the electrical conductivity of the Co-doped BCTCo perovskite is higher than that of the BCTb oxide at the same temperature in the air atmosphere. This may be a combined effect of the increase in both the oxygen ionic conductivity and electronic conductivity. On one hand, more oxygen vacancies have been created as a result of cobalt doping [21]. Furthermore, the size difference between cobalt and ceria ions at the grain boundaries results in different distortions of the surrounding lattices, leading to improved mocility of oxygen vacancies through the grain boundaries [22]. On the other hand, the electonic conductivity also can be promoted significantly by cobalt doping since the Co2+/Co3+ redox pair are present in the BCTCo perovskite lattice [23]. In addition, the BCTCo oxide exhibited higher conductivity in the air atmosphere than in the hydrogen atmospheres. For example, the electrical conductivity of the BCTCo perovskite at 800 C in the air and hydrogen atmospheres was 0.034 cm-1 and 0.024 scm-1, respectively.