The surface mechanism for the flexoelectric response in sodium bismuth titanate‐based ferroelectric ceramics.

The flexoelectric effect of the ferroelectric materials has been intensively studied in recent years. One unresolved issue in this field is that the measured flexoelectric coefficients in ferroelectrics are often several orders of magnitude greater than the values predicted by the theoretical studies. To understand the mechanism for this discrepancy, the flexoelectric response of the Na0.5Bi0.5TiO3–BaTiO3 (NBBT) ceramics of different compositions was systematically studied. We show that the measured flexoelectric response of the NBBT ceramics is mainly from the piezoelectric response of the spontaneously polarized surface in the ceramics. The surface effect can be reduced or removed by abrading the surface off or modifying the compositions of the surface. The thickness of the surface layer was found to be 10‐15 µm. We also show that the composition dependence of the flexoelectric response is mainly affected by the piezoelectric response of the surface layer, whereas the temperature dependence of the flexoelectric response of a composition is primarily influenced by the dielectric constant of the bulk. The mechanisms for the observations are discussed based on the origin of the surface layer. This work is important for the understanding of the mechanisms of the flexoelectric (or flexoelectric‐like) response in ferroelectrics. [ABSTRACT FROM AUTHOR]