Characterization of perovskite systems derived from Ba2In2O5□: Part II: The proton compounds Ba2In2(1−x)Ti2xO4+2x(OH)y [0≤x≤1; y≤2(1−x)]

The proton compounds Ba2In2(1−x)Ti2xO4+2x(OH)y [0≤x≤1; y≤2(1−x)] were prepared by reacting Ba2In2(1−x)Ti2xO5+x□1−x (0≤x≤1) phases with water vapor at ∼200 °C. For 0≤x≤0.20, the filling of oxygen vacancies is almost complete. For larger x values, it decreases significantly down to ∼30% only for x=0.7. The crystal structure of the end member Ba2In2O4(OH)2 (x=0) was reinvestigated by a combination of techniques including 1H and 2D NMR and electron, X-ray and neutron diffraction. The actual cell is eight times larger than that previously published. The structure analysis confirms that the sheet consisting of parallel chains of In(2)O4 tetrahedra and parallel rows of oxygen vacancies in the parent structure of Ba2In2O5□ has been converted into a In(2)O6 octahedral perovskite-like sheet. It demonstrates that the protons are bonded only to the O atoms around this In(2) site. increases, the change in reduced perovskite cell volume, concomitant with the water uptake, remains small for x<0.25 and negligible for larger x values. oton conductivity was measured between room temperature and 180 °C. The highest conductivity at 180 °C, σ180≈10−6 S cm−1, is observed for x∼0.3.