Influence of surface orientation on the photochemical reactivity of CaTiO 3

The orientations and surface structures of ferroelastic CaTiO 3 crystals within a polycrystalline ceramic were measured by electron backscatter diffraction and atomic force microscopy (AFM) respectively. Surfaces annealed at 1250°C in air are made up of a combination of facets with orientations near {100}, {110}, and {111} (indexed with reference to the cubic perovskite cell). The samples were immersed in an aqueous AgNO 3 solution and illuminated to photochemically reduce silver. Based on the amount of silver reduced on different surfaces, it was determined that surfaces with a {111} orientation had the greatest photocathodic reactivity, those with a {110} orientation had the least photocathodic reactivity, and surfaces with the {100} orientation had intermediate reactivity. While the {110} surfaces were essentially inert for photocathodic reduction, they were active for the photoanodic oxidation of Mn 2+ . Ferroelastic domains were observed to enhance and retard the photochemical reduction of silver on spatially alternating domains on 20% of the grains. However, domains had no influence on the reactivity of the other 80% and are therefore secondary to the surface orientation in determining the reactivity.