Barium cerate ($BaCeO_3$) related perovskite ceramics currently dominate the high-temperature proton conductor field. Unfortunately, these materials have very stringent environmental limitations necessitating the costly and complex conditioning or cleaning of the application feed-gas. Commercial realization has been hampered, in part, because of the reactivity of $BaCeO_3$ with $CO_2$, and to some extent $H_2O$. And sintered $BaCeO_3$ decomposed at a rate comparable to the powder samples. In this article, the chemical stability and the structural changes of $BaCe_{0.9-X}Y0.1La_XO_{3-delta}$ (X=0, 0.1, 0.2) have been systematically investigated in the atmosphere containing carbon dioxide ($CO_2$) and water vapor ($H_2O$). The sintering characteristics were studied in $1600^{circ}C$, sintered pellets disintegrate and decompose upon contacting boiling water on the surface only.