Effects of cobalt addition on structural, thermal and electrical properties of praseodymium-yttrium co-doped barium cerates

Effects of cobalt addition on structural, thermal and electrical properties of praseodymium-yttrium co-doped barium cerates have been investigated. Relative densities > 98 % have been achieved after sintering at 1400 A degrees C or 1500 A degrees C for only 1 h. All studied compounds are stable in ambient air up to the measured 900 A degrees C and, in reducing atmosphere (both wet and dry 5 % H-2-Ar) up to the measured 800 A degrees C. The Co-free sample (BaCe0.7Y0.2Pr0.1O3-delta) exhibits the highest conductivity of 1.21 x 10(-2) S cm(-1) at 700 A degrees C in air while the corresponding cobalt containing sample (BaCe0.7Y0.175Pr0.1Co0.025O3-delta) has a conductivity of 9.85 x 10(-3) S cm(-1) at 700 A degrees C in air. Cobalt addition allows the ability to retain much larger amounts of water to be retained as suggested by the higher conductivities obtained in wet hydrogen compared to the values in dry reducing atmosphere. This latter phenomenon is of special interest as it suggests the possibility of higher ionic conductivities in water-containing atmosphere and would benefit to intermediate- and high-temperature solid oxide fuel cells and/or electrolysers. The thermal expansion coefficients for the Co-free and Co-containing samples were around 12.0 x 10(-6) K-1 between 25 and 1000 A degrees C.