Optomechanical Mapping of Ferroelectric Domains and the Piezo-Photovoltaic Effect in Ba- and Ni-Doped (K0.5Na0.5)NbO3

The piezo-photovoltaic effect has been recently proposed as an analogy of the flexo-photovoltaic effect in noncentrosymmetric ferroelectrics that are also piezoelectric in nature. It has been demonstrated to boost the photovoltaic performance of ferroelectrics under applied uniaxial mechanical loads. The impact of the piezo-photovoltaic effect on ferroelectric domains, however, has not yet been studied. In this context, a nanoscale insight into mechanical as well as optomechanical control of domains in a novel bandgap-engineered ferroelectric, namely—KNBNNO ((K_0.5Na_0.5)NbO₃–2 mol% Ba(Ni_0.5Nb_0.5)O_3−δ), is provided. It is found that the applied mechanical force of 1 μN (pressure: 0.25 GPa) using a scanning probe tip evinces a 67% amplification in piezoresponse in the material, and on removing mechanical load, the material retains 33% higher piezoresponse than the pristine state. Mechanically induced property changes in the material are found to be strongly influenced by light illumination. Applied mechanical stress due to an atomic force microscopy (AFM) tip is highly nonuniform and can induce additional polarization via the flexoelectric effect which further enhances the photovoltaic charge screening.