Influence of the Magnitude of Ferroelectric Domain Polarization on the Photochemical Reactivity of BaTiO₃

The spontaneous polarization of domains in ferroelectric materials has been used to spatially separate photogenerated electrons and holes, reducing recombination and thereby improving the efficiency of photochemical reactions. Here, the influence of the magnitude of the polarization on photochemical reactivity is investigated. The magnitude of the out-of-plane component of the polarization was characterized by scanning Kelvin probe force microscopy (KFM). By examining crystals with orientations that deviate by only a few degrees from (001), two types of domains were identified: those with polarization vectors nearly perpendicular to the surface and those with polarization vectors nearly parallel to the surface. The photochemical reactivity was measured using topographic atomic force microscopy to determine the amount of Ag+ (Pb2+) that was photochemically reduced (oxidized) to Ag (PbO2) on the surface. For the reduction reaction, the reactivities of domains with polarizations nearly perpendicular to the surface were only about 3 times greater than the reactivities of the domains with polarizations nearly parallel to the surface, indicating that, for this reaction, the magnitude of the out-of-plane polarization is less important than its sign. For the oxidation of lead, only the domains with polarizations nearly perpendicular to the surface were reactive, indicating that for this reaction, both the sign and magnitude of the polarization are important.