Short-range structure of the brownmillerite-type oxide Ba2In2O5 and its hydrated proton-conducting form BaInO3H

Abstract

The vibrational spectra and short-range structure of the brownmillerite-type oxide Ba₂In₂O₅ and its hydrated form BaInO₃H, are investigated by means of Raman, infrared, and inelastic neutron scattering spectroscopies together with density functional theory calculations. For Ba₂In₂O₅, which may be described as an oxygen deficient perovskite structure with alternating layers of InO₆ octahedra and InO₄ tetrahedra, the results affirm a short-range structure of Icmm symmetry, which is characterized by random orientation of successive layers of InO₄ tetrahedra. For the hydrated, proton conducting, form, BaInO₃H, the results suggest that the short-range structure is more complicated than the P4/mbm symmetry that has been proposed previously on the basis of neutron diffraction, but rather suggest a proton configuration close to the lowest energy structure predicted by Martinez et al. [J.-R. Martinez, C. E. Moen, S. Stoelen, N. L. Allan, J. Solid State Chem., 180, 3388, (2007)]. An intense Raman active vibration at 150 cm⁻¹ is identified as a unique fingerprint of this proton configuration.