The origin of charged domains on the surface of ferroelastic BiVO4 co-doped with sodium and molybdenum

Ferroelastic BiVO₄ has charged surface domains, even though its crystal structure is non-polar. These charged domains can be detected by piezo-force microscopy and lead to spatially selective photochemical reactions. The photochemical reactivity of (Bi_0.96Na_0.04)(V_0.92Mo_0.08)O₄ is studied above and below the ferroelastic transition temperature to better understand the origin of charged ferroelastic domains. The results demonstrate that spatially selective reactivity occurs above the ferroelastic transition temperature, similar to what is observed below the transition temperature. Furthermore, when the sample is cooled after brief excursions above the transition temperature, the domains reform with a microstructure that is indistinguishable from what is observed before the transition. The results are consistent with the idea that inhomogeneous distributions of charged point defects, created by stress in the ferroelastic domains, lead to charged domains that promote spatially selective photochemical reactions. If these inhomogeneous defect distributions are not homogenized above the transition temperature, they can template the re-creation of the original domain microstructure after the transformation back to the ferroelastic phase.