Photochemical Approach to Analysis of Ferroelectric Transition in Ba_xSr_1-xTiO₃ Epitaxial Films

Abstract

When Sr1-xBaxTiO3 (0<x<1) epitaxial film is illuminated with UV-visible light (377 to 483 nm) in aqueous AgNO3 solutions, a photochemical reaction product of Ag is deposited on the film surface. The compositional dependences of the amount of Ag and band gap show an abrupt change at x=0.6, i.e., near Ba0.6Sr0.4TiO3, which has its Curie temperature near room temperature. On the basis of an analysis of these behaviors near the ferroelectric transition, it is found that ferroelectric and paraelectric domains coexist in the composition ratio range of x=0.5 to 0.7, as confirmed by X-ray diffraction.

Enhanced Photochemical Reactivity at the Ferroelectric Phase Transition in Ba1−xSrxTiO3

“…This is not consistent with the observations, and therefore we conclude that the change is band gap is not a dominant factor in determining the composition dependence of the reactivity. However, it should also be mentioned that the composition dependence of the photochemical reduction of silver in nanostructured Ba 1− x Sr x TiO 3 thin films, which do not exhibit band bending, was explained by changes in the band gap 27 . For that case, both the composition dependence of the reactivity and the band gaps differed substantially from the bulk material described here 27 …”

“…However, it should also be mentioned that the composition dependence of the photochemical reduction of silver in nanostructured Ba 1Àx Sr x TiO 3 thin films, which do not exhibit band bending, was explained by changes in the band gap. 27 For that case, both the composition dependence of the reactivity and the band gaps differed substantially from the bulk material described here. 27 Polarization within the domains changes dramatically as a function of composition and this also has the potential to affect the reactivity.…”

“…27 For that case, both the composition dependence of the reactivity and the band gaps differed substantially from the bulk material described here. 27 Polarization within the domains changes dramatically as a function of composition and this also has the potential to affect the reactivity. Room temperature polarization data reported by Ianculescu et al 19 indicates that the polarization decreases by about 1/3, from 26 to 17.5 mC/cm 2 , as the Sr content increases from x 5 0 to x 5 0.3.…”

“…[20][21][22][23][24][25] The positions of the conduction band edges are also similar, with the BaTiO 3 conduction band edge being 50 mV higher than that of SrTiO 3 . 26 Ohara et al 27 reported the photochemical reduction of silver on a thin film that was compositionally graded in one spatial dimension from pure SrTiO 3 to pure BaTiO 3 . The amounts of silver were related to changes in the band gap and they found that the transition from the ferroelectric to nonferroelectric phase occurred over a wide composition range.…”

Composition Dependence of the Photochemical reduction of Ag by Ba1−xSrxTiO3

“…Samantaray et al 42 also reported a similar smooth increase with strontium content from 3.25 eV to 3.55 eV. Ohara et al 43 reported that the band gap initially decreases with increasing strontium content (from 0 < x < 0.4), including an abrupt 125 mV step change at the cubic to-tetragonal transition. The grain size, film thickness, and lattice strain can all influence the observed band gaps in these films and this is likely to account for the inconsistency of the reports.…”