No abstract

Ba1-xSr x TiO3 solid solutions with x = 0−1 were used to photochemically reduce aqueous Ag+ to Ag0. 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.

Optical absorption and reflectance spectroscopy have been used to monitor the photochemical reactivity of Ba1−xSrxTiO3 solid solutions with aqueous solutions containing methylene blue. Atomic force microscopy indicates that methylene blue is reduced on the surfaces of domains that have a positive surface polarization. The results indicated that SrTiO3 and BaTiO3 have similar reactivities. As the second component is added to either of the pure materials, the reactivity decreases. However, there is a sharp maximum in reactivity at the tetragonal‐to‐cubic phase boundary. This is attributed to the anomalously high dielectric constant at this composition that increases the width of the space charge region and charge carrier separation in the near surface region.