Flexoelectricity in low densification materials and its implication

Abstract

Coupling between the strain gradient and the electric polarization, also named flexoelectricity, is a fundamental but often overlooked property in solid dielectrics. The past ten years has witnessed its great potential in sensing and actuating applications, especially in nanomaterials or nanostructures. The recently discovered giant flexoelectricity in barium strontium titanate (BST) perovskite above its Curie temperature has boosted the research interests on flexoelectricity to a new height. The possible interpretation of the enhanced flexoelectricity in BST was initially attributed to the non-crystalline polar-phases or polar nano-regions existing in the perovskites, then to the inner micro strain generated from the material densification process. In this paper, we analyzed the origin of flexoelectricity in this kind of materials by using both analytical mechanics method and finite element simulation method. Our results suggested the inner micro defect generated during the material densification process would weaken the flexoelectricity of the materials. The observed polarization in the studied materials was likely induced by other mechanisms rather than the pure flexoelectricity.

Advancements and Prospects of Flexoelectricity

“…To indirectly measure the strain gradient, a highresolution displacement sensor is employed. 19 This sensor accurately detects and quantifies the displacement occurring in the material due to the strain gradient induced by the applied bending deformation. The surface of the rectangularly shaped specimen is coated with electrodes.…”

“…Based on the assumption of the neutral plane of the beam, the bending effect induces tension above the neutral plane and compression below it, resulting in a strain gradient uniformly distributed across the thickness direction of the cantilever beam. To indirectly measure the strain gradient, a high-resolution displacement sensor is employed . This sensor accurately detects and quantifies the displacement occurring in the material due to the strain gradient induced by the applied bending deformation.…”

“…Conversely, it also encompasses the coupling between the electric field gradient and the mechanical stress, known as the converse flexoelectric effect. These two complementary phenomena characterize the bidirectional relationship between strain and polarization, as well as between electric field and stress, within the framework of flexoelectricity. − When subjected to nonuniform external forces, a nonconductive material undergoes deformation, resulting in the generation of a strain gradient within its structure, subsequently leading to the induction of a polarization phenomenon. Additionally, opposing charges of positive and negative nature manifest on the surfaces facing opposite directions.…”

Flexoelectric materials and their related applications: A focused review

“…(ii) Strain gradient is inversely proportional to the material size, making the nanoscale flexoelectricity extremely large [14][15][16]. Such characteristic is called size effect or scaling effect, and has already been utilized in many nanostructures for sensing and actuating applications [17,18].…”

Bending and Vibration Analysis of Flexoelectric Beam Structure on Linear Elastic Substrates

“…There is a large market for smart devices at the nano-scale, when the flexoelectric effect, which is neglected at the macro-scale, plays an increasingly vital role due to its high electromechanical coupling. The flexoelectric effect is a kind of electromechanical coupling caused by strain gradients or non-uniform deformations [1][2][3][4], and this electromechanical phenomenon is size-dependent at the nano-scale [5]. Therefore, it is essential to understand and analyze the flexoelectric effect in nanoscale materials and structures.…”