Design Of Flexoelectric Piezoelectric Materials

Conventional piezoelectric ceramics lose their piezoelectric properties near the Curie temperature(Tc),which limits their application at high temperatures.One approach to resolving this issue is to design flexoelectric piezoelectric composites by exploiting the flexoelectric effect of the ferroelectric materials.In this work,an experimental study on two designs of flexoelectric metamaterials is demonstrated.When a ferroelectric ceramic wafer is placed on a metal ring or has a domed shape,which is produced through the diffusion between two pieces of ferroelectric ceramic of different compositions at high temperatures,an apparent piezoelectric response originating from the flexoelectric effect can be measured under a stress.The apparent piezoelectric response of the materials based on the designs can be sustained well above Tc.This study provides an approach to designing materials for high-temperature electromechanical applications.Point-ring design is proposed by placing a ferroelectric ceramic wafer on a metal ring,an apparent piezoelectric response can be measured when the ceramic wafer is bent by a point force to generate the flexoelectric response.A simple derivation suggests that an apparent d33 originating from the flexoelectric effect can be generated,if a stress is applied to the ceramic wafer.The apparent piezoelectric d33 for BTO ceramic is measured approximately 256pC/N of point-ring design,the magnitude of the flexoelectric coefficient is consistent with most of the tested ferroelectric oxides.The apparent piezoelectric response for the BTO ceramic is existed well above the Curie temperatures of the ferroelectric materials,approximately 167pC/N even at 300?.To simplify the point-ring design,a curvature structure was produced through the diffusion between two ceramic wafers of different compositions at high temperatures(point-plane design),a bending deformation and the flexoelectric effect can be generated in the sample with curvature under a stress without the support of a ring.NBBT6 ceramics were diffused with NBBT8 and BST ceramic,respectively.The domed NBBT6,NBBT8 and BST ceramic wafers exhibit an apparent piezoelectric response well above the Curie temperatures of the ferroelectric materials.Even at 400?,the apparent d33 ceramic is 10pC/N for NBBT6 ceramic wafer and 7pC/N for NBBT8,the Tc of the BST ceramic is lower than room temperature,the material exhibits a substantial apparent d33 of 1pC/N until 200?.