Composition Dependence of the Photochemical reduction of Ag by Ba_(1-X)Sr_xTiO3

摘要

Ba_(1-x)Sr_xTiO3 solid solutions with x = 0-1 were used to photochemically reduce aqueous Ag~+ to Ag~0. The reduction of Ag on BaTiO3 is spatially selective and correlated to the locations of positive ferroelectric domains. On SrTiO3, silver reduction is spatially uniform. As strontium is added to BaTiO3, there is a continuous change from spatially localized to uniform reactivity that is complete at x > 0.27. The relative heights of the silver deposits, as measured by atomic force microscopy, were used to quantify the relative reactivities. A local maximum in the reactivity is observed at x = 0.26, which is near the cubic-tetragonal phase boundary. The change from spatially selective to spatially uniform reactivity is associated with decreased polarization as the strontium concentration increases. The local maximum in reactivity near the phase boundary is associated with an anomalously high dielectric constant at this composition that enlarges the space-charge region. The results are consistent with the idea that the width of the space-charge region is an important factor in determining the photochemical reactivity.