Converse flexoelectricity with relative permittivity gradient

Abstract

Flexoelectricity represents the linear relationship between the strain/electric gradient field and the induced electric polarization/mechanical stress in dielectric materials. This electro-mechanical behavior is important for prospective applications due to its size effect and other advantages. In this work, a converse flexoelectric effect is generated by the designed permittivity gradient with Ba0.67Sr0.33TiO3 ceramic powder and the substrate. The equivalent piezoelectric effect of the gradient composite is obviously increased by converse flexoelectricity. This study opens up an avenue for prospective sensing and actuating approaches for both piezoelectric and non-piezoelectric dielectric materials with relative permittivity gradients and uniform geometric structures.

Universal converse flexoelectricity in dielectric materials via varying electric field direction

“…F m f gand F q � � are the mechanical and electrical force vectors. The details of the material matrices, stiffness matrices, and force vectors are given in Appendix A. Equations (34) and (35) are solved in a coupled sense for computing the potential distribution in the domain and displacement field due to this potential.…”

“…The direct and converse flexoelectric effects being the manifestations of a single electromechanical coupling, as argued in references [9,48], tend to influence one another by changing boundary conditions. This can be also be understood by inspecting the governing equations (Equation (34) and (35)) of the flexoelectricity, where the coupling stiffness matrix used in the converse flexoelectric effect is the same as that in direct effect. Thus, the pattern I can generate high displacements locally, but fails to surpass the performance of the conventional pattern of electroding (top and bottom surface fully covered by electrodes) in actuating the entire target surface.…”

“…For this purpose, cantilever-shaped energy harvesters and sensors, due to the presence of nonuniform strain in bending, have been vastly investigated in the past [22][23][24][25][26][27][28][29][30][31][32][33] Variable mechanical characteristics can result in varying strain distribution within the domain. A few studies have suggested the use of special composite materials to achieve variation in mechanical properties and thereby a strain gradient [34][35][36][37][38][39]. This method eliminates the need for special designs and dimensions of the devices to be employed, however, it requires an additional effort at manufacturing stage for compositional variation.…”

Flexoelectric Poling of Functionally Graded Ferroelectric Materials

“…Recently, graded composition has been shown to have a strong flexoelectric coupling in regular shaped geometries, eliminating the requirement of a specialized shape. [ 30,31 ]…”

“…Recently, graded composition has been shown to have a strong flexoelectric coupling in regular shaped geometries, eliminating the requirement of a specialized shape. [30,31] Although the relevant literature available and discussed so far reveals the possibility of flexoelectricity to be a viable candidate for polarization switching of ferroelectric materials, to the best of our knowledge, there is no study explicitly considering flexoelectricity as a practicable solution for piezoelectric poling by purely mechanical means. Therefore, we present an exhaustive numerical simulation study to analyze the polarization obtained through flexoelectric coupling in unpoled samples as an agent for permanent poling of the samples, solely by mechanical means.…”