Comparative studies were performed on variations in the ABO 3 perovskite structure, chemical stability in a CO 2 -H 2 gas atmosphere, and electrical conductivity measurements in air, hydrogen, and humidity-involving gas atmospheres of monophase orthorhombic Ba 1−x Sr x Ce 0.9 Y 0.1 O 3−δ samples, where 0 < x < 0.