Oxygen-ion and proton conductivity in the Ba3InGa2O7.5 complex oxide with incomplete oxygen sublattice

The Ba3InGa2O7.5 complex oxide, possessing the perovskite-related structure with structural oxygen vacancies, was first synthesized by the solid state method. The phase was found to be characterized by monoclinic symmetry (sp. gr. P2/c) with the following unit cell parameters: a = 7.942(1) Å, b = 5.868(5) Å, c = 18.201(6) Å, b = 91.52(9). Comprehensive investigations of electrical properties were carried out; ceramic material based on the complex oxide was shown to be a predominantly ionic conductor in the temperature range 450–900 oC. The conductivity is due to oxygen-ion transfer in dry conditions and oxygen-ion and proton transfer in wet atmosphere. The proton conductivity value is 4.5·10–5 S/cm, and the proton transport number is ~50% at 700 oC in wet air; at lower temperatures, proton transport becomes dominant. Prolonged treatment of the sample in water vapors below 450 oC leads to hydrolysis decomposition.