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Relaxor ferroelectrics have applications in transducers and capacitors owing to their dielectric relaxation. Although the existence of polar nanoregions (PNRs) inside the relaxor ferroelectrics contributes to enhancing the dielectric response, the dielectric relaxation mechanism remains unclear in the wide frequency range from kHz to THz. In this study, we investigated the frequency-dependent (103-1012 Hz) dielectric properties using ultrafast phase-field simulations. The dielectric response is divided into the matrix response, the "collinear" PNR response, and the "non-collinear" PNR response. Among them, the collinear PNR response accounts for 90% of the dielectric constant enhancement. The response behavior of collinear PNRs has a higher frequency limitation than that of non-collinear PNRs. The different relaxation times of the collinear PNR lead to a corresponding distinct rotation for the polar vectors. Finally, we investigate the different response behaviors of the polarization in the PNR from the aspect of energy barriers. This study not only promotes the understanding of wide-range frequency-dependent dielectric relaxation processes but also guides the design of ultrafast relaxor ferroelectric devices in the future. [ABSTRACT FROM AUTHOR]

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In order to develop the application of energy storage ceramics, the dielectric properties and energy storage density of Ba0.1Sr0.9Zr0.18Ti0.82O3 ceramics (BSZT-118) prepared by the modified sol–gel process were researched under different temperatures under electric field. The results show that the dielectric constant of BSZT-118 is consistent with Johnson's formula based on Devonshire phenomenological theory, and the anharmonic constant (α) increases as the temperature rises. The energy storage density of BSZT-118 is influenced by the electric field and temperature. With the increase in temperature, the storage density of BSZT decreases and the fluctuation of storage density increases under electric field. The conduction mechanism of BSZT-118 is mainly space charge-limited conduction (SCLC) below 60 °C, and it is mainly Ohmic conduction above 60 °C. [ABSTRACT FROM AUTHOR]

Abstract A phenomenological Landau-Devonshire theory is applied to construct the thermodynamic potential of (110) oriented Ba(Zr 0.08 Ti 0.92)O 3 thin film and investigate the phase transition, ferroelectric, dielectric and piezoelectric properties. Three ferroelectric phases, such as tetragonal a 1 phase, orthorhombic a 2 c and triclinic γ phase are stable in "misfit strain-temperature" phase diagram. Two triple points are found in the phase diagram and 90 ° polarization switching can occur directly between tetragonal a 1 phase and orthorhombic a 2 c phase. Complicated phase transitions are induced by the electric field in triclinic γ phase due to the nonlinear coupling terms appeared in the thermodynamic potential. The longitudinal piezoelectric coefficient of (110) oriented Ba(Zr 0.08 Ti 0.92)O 3 thin film is smaller than that of (001) oriented film. Moreover, negative longitudinal piezoelectric coefficient can be obtained in triclinic γ phase. Highlights • Tetragonal a 1 phase, orthorhombic a 2 c phase and triclinic γ phase are stable in phase diagram. • Complicated phase transitions are induced in triclinic γ phase by electric field. • Negative longitudinal piezoelectric coefficient is obtained in triclinic γ phase. [ABSTRACT FROM AUTHOR]

The challenge of designing new tunable nonlinear dielectric materials with tailored properties has attracted an increasing amount of interest recently. Herein, we study the effective nonlinear dielectric response of a stochastic paraelectric-dielectric composite consisting of equilibrium distributions of circular and partially penetrable disks (or parallel, infinitely long, identical, partially penetrable, circular cylinders) of a dielectric phase randomly dispersed in a continuous matrix of a paraelectric phase. The random microstructures were generated using the Metropolis Monte Carlo algorithm. The evaluation of the effective permittivity and tunability were carried out by employing either a Landau thermodynamic model or its Johnson's approximation to describe the field-dependent permittivity of the paraelectric phase and solving continuum-electrostatics equations using finite element calculations. We reveal that the percolation threshold in this composite governs the critical behavior of the effective permittivity and tunability. For microstructures below the percolation threshold, our simulations demonstrate a strong nonlinear behaviour of the field-dependent effective permittivity and very high tunability that increases as a function of dielectric phase concentration. Above the percolation threshold, the effective permittivity shows the tendency to linearization and the tunability dramatically drops down. The highly reduced permittivity and extraordinarily high tunability are obtained for the composites with dielectric impenetrable disks at high concentrations, in which the triggering of the percolation transition is avoided. The reported results cast light on distinct nonlinear behaviour of 2D and 3D stochastic composites and can guide the design of novel composites with the controlled morphology and tailored permittivity and tunability. [ABSTRACT FROM AUTHOR]