Motivated by the goal of improving the proton conduction in the brownmillerite Ba2In2O5 we are investigating the role of isovalent substitution at the indium sites. In particular we have prepared Ba2In2-xMxO5, x = 0.1 (M = Ga and Y) and x = 0.3 (Y). Significant differences in the de-hydration behaviour of the hydrated, Ba2In2-xMxO4(OH)2, phases are seen in TG-DSC data, suggesting the ¿dopant¿ ions strongly influence the proton environment. Here we request 5 days beam-time to study the hydration and de-hydration reactions of 4 samples, the parent Ba2In2O5 and 3 substituted derivatives, in-situ using the controlled humidity conditions cell. We will also collect total-scattering data at RT on 8 samples (as-prepared and fully deuterated versions). In particular we aim to discern the local environments of the In and substituent ions, and locate deuteron sites in the materials.