Nonlinear dielectric properties of paraelectric-dielectric composites described by a 3D Finite Element Method based on Landau-Devonshire theory

The local field inhomogeneity generated by the interfaces between dissimilar phases plays a major role on the electrical properties of ferroelectric-based composites. This aspect was rarely investigated, because it requires advanced modeling tools. In the present work, a 3D Finite Element Method combined with Landau-Devonshire theory was developed for computing local fields in order to describe the role of realistic microstructures on the electrical response. Various combinations of materials and interconnectivities in paraelectric-based di-phase composites (phases randomly mixed, 0-3 connectivity or 1-3 connectivity) were analyzed and some valuable solutions for providing the most promising tunability properties are proposed. A decrease of tunability and permittivity when increasing the concentration of the dielectric component in composites with randomly distributed phases and in ones with 0-3 connectivity (paraelectric inclusions in a dielectric matrix), often reported experimentally, was obtained by this approach. For other configurations like 0-3 and 1-3 connectivity with dielectric inclusions in a paraelectric matrix, the simulations predicted comparable tunability values as in single phase paraelectrics. The best tunability properties are predicted for 1-3 connectivity with dielectric inclusions having the long axis perpendicular to the direction of the applied field, due to a favorable distribution of the local electric field within the system. Therefore, the proposed numerical method allows design composites with tailored permittivity and tunability by local field engineering. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.