This proposal intends to study the recently found important role of hole trapping in perovskite structure titanates. As a result of hole trapping and its consequences, insulating material may be obtained after equilibrium at lower partial oxygen pressure than previously considered possible. This proposed program will focaus on undoped and acceptor-doped BaTiO3 and SrTiO3, and will conduct experiments to further the understanding of the equilibrium defect chemistry of the perovskite titanates and its rel;ationship to properties of technological interest. Second part of the proposed program will be focussed on the defect chemistry and charge transport of perovskite-related oxides, specifically of the brownmillerite A2B2O5 structure and based on indium, gallium, and related elements. %%% This proposed study pursues the recently found important role of hole trapping in perovskite related oxides. It has significant implications with respect to the multilayer ceramic capacitor market. This study aims to pursue the investigation into to the defect chemistry and its relationship to properties of technological interest. Second part of this study will investigate the origin of the high levels of ionic conductivity in oxygen- deficient variants of the perovskite structure such as the brownmillerite structure of A2B2O5. This study will have important contributions to the understanding of materials used in devices of technological importance.