Stability of AB{prime}{sub 1/2}B{double{underscore}prime}{sub 1/2}O{sub 3} mixed perovskite proton conductors

Several mixed perovskites of the type A{sub 2}B{prime}B{double{underscore}prime}O{sub 6} (AB{prime}{sub 1/2}B{double{underscore}prime}{sub 1/2}O{sub 3}), where A is Ba{sup +2} and B{prime} and B{double{underscore}prime} are trivalent and pentavalent ions, respectively, were synthesized by calcining requisite mixtures of BaCO{sub 3}, B{prime}{sub 2}O{sub 3}, and B{double{underscore}prime}{sub 2}O{sub 5} in air. X-ray diffraction confirmed the formation of the perovskite phase in each of the samples synthesized. The as-calcined powders were boiled in water to examine their stabilities in water. All mixed perovskites were found to be stable. By contrast, BaCeO{sub 3} and BaPrO{sub 3} decomposed when boiled in water while BaZrO{sub 3} was found to be stable. Madelung energies of simple and mixed perovskites were computed. The higher stability of mixed perovskites compared to simple perovskites of the type ABO{sub 3}, such as BaCeO{sub 3} and BaPrO{sub 3}, where B is a tetravalent ion, was rationalized on the basis of lower Madelung energies of mixed perovskites.