Electrical conductivities and chemical stabilities of mixed conducting pyrochlores for SOFC applications

Pyrochlores with praseodymium as the A-site cation and zirconium, tin, cerium and manganese cations on the B-site were prepared in air and their electrical conductivities were investigated as a function of oxygen partial pressure and temperature. Pure Pr2Zr2O7±δ as well as samples modified on the B-site with 5% Mn or 20% Ce show conductivities, which are lower than 2×10−3 S/cm at 1000°C in H2/H2O atmospheres. Electronic p-type conductivity was indicated for these materials in oxygen/nitrogen mixtures. The electrically conducting pyrochlore solid solutions Gd2TiMoO7±δ and Gd2Ti0.6Mo1.4O7±δ were synthesised and investigated in 1% H2/3% H2O/96% N2. No formation of a new phase by reaction with YSZ was indicated after exposure to this atmosphere at 1000°C for 1000 h. Pr2Sn2O7±δ modified with 5% indium on the B-site exhibited a conductivity in air of 6.5×10−3 S/cm at 1000°C. The pure material was found to decompose in mixtures of 9% H2/3% H2O/88% N2.