fig6

Figure 6. Flexoelectricity-driven photovoltaic effects in oxides and crystals. (A) Schematic illustration of flexoelectric polarization at polymorphic phase boundaries in BiFeO₃ thin films. (B) Conductive AFM photocurrent mapping of phase boundaries. (C) PFM phase image of BiFeO₃ thin films showing polymorphic domain structures. (A-C) Reproduced with permission^[20]. Copyright 2015, Springer Nature; (D) Schematic illustration of bending-induced strain gradients in freestanding membranes. (E) Calculated strain distribution during bending. (F and G) Schematics of polarization and flexoelectric fields in (F) downward- and (G) upward-polarized BiFeO₃ membranes under bending; (H and I) Band diagrams of bent BiFeO₃ membranes in (H) downward- and (I) upward-polarized states. (D-I) Reproduced with permission^[29]. Copyright 2020, Springer Nature; (J) Schematic of the experimental setup for flexo-photovoltaic measurements using AFM-tip loading. (K) Side-illumination geometry for photocurrent measurements. (L) Photocurrent collected by a conductive AFM tip under a high loading force on the SrTiO₃ (001) surface. (M) Photocurrent response on the TiO₂ (100) surface under a tip loading force. (N) Dependence of the short-circuit current on the applied loading force. (O) Photocurrent modulation under on/off laser illumination. (J-O) Reproduced with permission^[30]. Copyright 2018, American Association for the Advancement of Science. AFM: Atomic force microscopy; PFM: piezoresponse force microscopy; LSMO: La_0.67Sr_0.33MnO₃; BFO: BiFeO₃; PDMS: polydimethylsiloxane.