Piezoelectric mimicry of flexoelectricity

Abstract

The origin of "giant" flexoelectricity, orders of magnitude larger than theoretically predicted, yet frequently observed, is under intense scrutiny. There is mounting evidence correlating giant flexoelectric-like effects with parasitic piezoelectricity, but it is not clear how piezoelectricity (polarization generated by strain) manages to imitate flexoelectricity (polarization generated by strain gradient) in typical beam-bending experiments, since in a bent beam the net strain is zero. In addition, and contrary to flexoelectricity, piezoelectricity changes sign under space inversion, and this criterion should be able to distinguish the two effects and yet "giant" flexoelectricity is insensitive to space inversion, seemingly contradicting a piezoelectric origin. Here we show that, if a piezoelectric material has its piezoelectric coefficient be asymmetrically distributed across the sample, it will generate a bending-induced polarization impossible to distinguish from true flexoelectricity even by inverting the sample. The effective flexoelectric coefficient caused by piezoelectricity is functionally identical to, and often larger than, intrinsic flexoelectricity: the calculations show that, for standard perovskite ferroelectrics, even a tiny gradient of piezoelectricity (1% variation of piezoelectric coefficient across 1 mm) is sufficient to yield a giant effective flexoelectric coefficient of 1 $\mu$C/m, three orders of magnitude larger than the intrinsic expectation value.

References in corpus (7)

• Strain gradient induced polarization in SrTiO3 single crystals
• Breaking of macroscopic centric symmetry in paraelectric phases of ferroelectric materials and implications for flexoelectricity
• Flexoelectric effect in finite samples
• Origin Of the enhanced flexoelectricity of relaxor ferroelectrics
• Surface control of flexoelectricity
• Erratum: Size-dependent piezoelectricity and elasticity in nanostructures due to the flexoelectric effect[PHYSICAL REVIEW B 77, 125424 (2008)]
• Nonlinear Flexoelectricity in Non-centrosymmetric Crystals

Cited by in corpus (6)

• Does Flexoelectricity Drive Triboelectricity?
• Flexoelectret: An Electret with Tunable Flexoelectric-like Response
• Inverse flexoelectret effect: bending dielectrics by a uniform electric field
• Twin Boundary Mediated Flexoelectricity in LaAlO${}_3$
• Size effect of soft phonon dispersion law in nanosized ferroics
• Giant Superelastic Piezoelectricity in Flexible Ferroelectric $BaTi{O}_3$ Membranes