Phenomenological study of inhomogeneous interfacial ferroelectrics

摘要

Inhomogeneity in ferroelectrics can exist as undesirable defects in the single crystalline structure or as designable factors in the composite structure. Surface or interface is inhomogeneous in nature, and superlattices or mixed-phases are inhomogeneous under plan. Effects of the inhomogeneous interfacial layer on ferroelectric nonlinearity have been investigated using a time-dependent Ginzburg-Landau model based on phenomenological equation for a two-dimensional lattice of ferroelectric unit cells. The simulation is based on Ba_(0.8)Sr_(0.2)TiO_3 (BST) with and without the inhomogeneous interfacial layer, e.g., nonswitchable fixed dielectric, switchable linear dielectric, or switchable nonlinear dielectric, and with and without Ginzburg-type gradient effect originated from the interactions between the BST and interfacial layers. Homogenization of the inhomogeneous systems is realized by the gradient effect allowing the gradual variation in polarization between the neighboring unit cells, and it heavily depends on the dielectric type of the interfacial layer-whether or not the gradient effect is applied to the interfacial layer. Effects of frequency, electric field type, depolarization, lattice strain, temperature, and thickness on the inhomogeneous nonlinearity are discussed.