Fig. 3: Phenomenological model for the large electric-field-induced strain.
From: Origin of giant electric-field-induced strain in faulted alkali niobate films
a Schematic of PF-KNN thin film cross-section showing polarization states without an external electric field. The localized charge and strain cause symmetry lowering distortion resulting in the in-plane rotation of polarization in the vicinity of PFs and the magnitude of this distortion decreases with increasing distance from the PFs. DFT model showing the b, in-plane and c, out-of-plane structural distortions adjacent to the PF. d Schematic of a PF-KNN thin film cross-section showing polarization states under an electric field, E. The polarization aligns with the direction of E which is facilitated and mediated by the migration of polaronic charges. Charge migration destabilizes the structure at the PFs including the variation in the Nb valence and lattice deformation due to the electron-charge-induced Coulombic forces. When the field is removed, the polarization configuration returns to its original form as in a due to the coupling of polaronic charge with their trapping centers at the PFs. The ionic displacements at the PFs cause large reversible strains in the vicinity of PFs as depicted in e.
