Morphotropic phase boundary-like properties in a ferroelectric-paraelectric nanocomposite

High dielectric and piezoelectric properties of solid-solution ferroelectrics around a morphotropic phase boundary (MPB) have attracted considerable attention in the last 60 years. Previous studies on MPB generally focused on a phase boundary between two ferroelectric phases, attributing enhanced dielectric/piezoelectric response to both intrinsic and extrinsic contribution. However, contribution from interfacial effects among the regions with different ferroelectric phases has not been fully considered. Therefore, it is valuable to study dielectric/piezoelectric responses in a ferroelectric-paraelectric system, where interfaces among different polar states may have a strong influence on the averaged free energy profile. In this paper, the piezoelectric response of a ferroelectric-paraelectric nanocomposite, i.e., the xSrTiO₃-(1-x)BaTiO₃ system, is systematically studied. By phase-field simulations, domain evolution of the xST-(1-x)BT composite poled along the [001] and [011] axis is presented with respect to the applied electric field. The piezoelectric strain coefficient of the xSrTiO₃-(1-x)BaTiO₃ composites is found to first increase and then decrease with increasing the parameter x, which is similar to that observed in ferroelectric solid solutions with a MPB. Finally, the temperature-dependent piezoelectric responses of the composites are also simulated, where a compromise between the roomerature piezoelectricity and the thermal stability is observed. This work may benefit the design of the ferroelectric-paraelectric composite.