Studies on the nonlinear dielectric response in ferroelectric–dielectric composite system

The nonlinear dielectric response (NDR) of Bi3.25La0.75Ti3O12–Al2O3 systems has been studied. To reveal the effects of the dielectric layer (DL) systematically, a method based on the equivalent circuit analysis and parametric study is proposed. The consistency between the calculated results and the experimental results manifests the validity of the method. In addition to the Rayleigh coefficients varying monotonically with the capacitance of DL, it is revealed that the slope between the real and the imaginary parts of the complex capacitance under different ac voltages is related to the relative loss values of DL and the ferroelectric layer. The frequency dependence of the NDR parameters is also discussed. The method established in this work is useful for research on the devices based on the ferroelectric–dielectric system and the ultra-thin ferroelectric films.