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Electric field-induced antiferroelectric-ferroelectric phase transition and the associated nonlinear dielectric behavior in particulate composites are investigated for achieving a high dielectric capacity. A phenomenological thermodynamic model based on the Landau theory is first developed to discuss the generic phenomena of a temperature-electric field phase diagram, coexistence of antiferroelectric and ferroelectric phases, field-induced antiferroelectric-ferroelectric phase transition, and nonlinear dielectric behavior. The model is then used to carry out the phase field simulation of particulate nonlinear dielectric composites. It is found that the composites exhibit nonlinear dielectric behaviors, and the depolarization field in the composites helps reduce the dielectric hysteresis and enhance the reversibility of antiferroelectric-ferroelectric phase transitions, which are desired for energy storage applications. The simulations also reveal the underlying domain-level mechanisms for nucleation and growth processes of the phase transitions. It is shown that the macroscopic properties of the composites sensitively depend on the directional alignment of the antiferroelectric filler particles, and thus the filler morphology is an effective control variable in designing nonlinear dielectric composites. [ABSTRACT FROM AUTHOR]

Control of magnetic permeability through voltage promises to create novel electronic devices, such as voltage tunable inductors. The relationship between the structure and property of voltage tunable inductors comprising of magnetoelectric Metglas/PZT composites and the underlying domain-level mechanisms are investigated using theoretical analysis, computer simulation, and complementary experiments. A theoretical model is developed to analyze the roles of material anisotropy, inductor shape, and stress in controlling the Metglas permeability and its tunability. The analysis reveals key roles played by stress-induced anisotropy and the resultant ground magnetization state, and predicts two stress-dependent regimes of inductance tunability. The theory is validated using systematic experiments. The experimental results are used to determine the material and physical parameters. To further elucidate the underlying domain-level mechanisms responsible for controlling the behavior of voltage tunable inductor, phase field modeling is employed to simulate domain microstructures and magnetic permeability of Metglas/PZT composites under varying voltage. The computational results confirm the two regimes of inductance tunability and the controlling role of stress-induced anisotropy. The findings suggest engineering of internal bias stress as an effective means to optimize the inductance tunability of magnetoelectric Metglas/PZT composites. [ABSTRACT FROM AUTHOR]