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Flexoelectricity is a property of a dielectric material whereby it exhibits a spontaneous electrical polarization induced by a strain gradient. Flexoelectricity is closely related to piezoelectricity, but while piezoelectricity refers to polarization due to uniform strain, flexoelectricity refers specifically to polarization due to strain that changes from point to point in the material. This nonuniform strain breaks centrosymmetry, meaning that unlike in piezoelectiricty, flexoelectric effects can occur in centrosymmetric crystal structures. Flexoelectricity is not the same as Ferroelasticity. Inverse flexoelectricity, quite intuitively can be defined as generation of strain gradient due to polarization. Similarly extending on that, Converse flexoelectricity would refer to the process where a polarization gradient induces strain in a material.
The electric polarization due to mechanical stress in a dielectric is given by
where the first term corresponds to the direct piezoelectric effect and the second term corresponds to the flexoelectric polarization induced by the strain gradient.
Here, the flexoelectric coefficient, , is a fourth-rank polar tensor and is the coefficient corresponding to the direct piezoelectric effect.
- Pavlo Zubko, Gustau Catalan, and Alexander K. Tagantsev (2013). "Flexoelectric Effect in Solids". Annual Review of Materials Research. 43: 387–421. doi:10.1146/annurev-matsci-071312-121634. hdl:10261/99362.CS1 maint: multiple names: authors list (link)
- Abdollahi A, Domingo N, Arias I, Catalan G (2019). "Converse flexoelectricity yields large piezoresponse force microscopy signals in non-piezoelectric materials". Nature Communications. 10: 1266. doi:10.1038/s41467-019-09266-y.