A phenomenological multi-axial constitutive law for switching in polycrystalline ferroelectric ceramics

A phenomenological constitutive law for ferroelectric switching due to multi-axial mechanical and electrical loading of a polycrystalline material is developed. The framework of the law is based on kinematic hardening plasticity theory and has a switching surface in the space of mechanical stress and electric field that determines when non-linear response is possible. The size and shape of the switching surface in a modified electric field space remains fixed during non-linear behavior but its center moves around and thus is controlled by a kinematical hardening process. In general, the remanent polarization and the remanent strain are used as the internal variables that control how the center of the switching surface moves. However, the form presented in this paper has a one-to-one relationship between the remanent strain and the remanent polarization, simplifying the constitutive law and allowing remanent polarization to be used as the only internal variable controlling the kinematic effects. The constitutive law successfully reproduces hysteresis and butterfly loops for ferroelectric ceramics. The hysteresis and butterfly loops respond appropriately to the application of a fixed compressive stress parallel to the electric field. In addition, the law successfully handles remanent polarization rotation due to the application of electric field at an angle to the polarization direction.     

Domain switching in ferroelectric single crystal/ceramics under electromechanical loading

Domain switching in PMN-PT single crystal and PZT-5 ceramics under electromechanical loading were studied in two different ways. For the single crystal, domain switching was in situ investigated with polarized light microscopy. A 90° domain-switching zone was observed near the crack tip and the size of the switching zone changed with the acuity of the crack tip. For PZT-5 ceramics, domain switching under orthogonal electromechanical loading (E₃ and compressive stress σ₁₁) was studied by measuring the hysteresis loops, butterfly curves and reversed butterfly curves (₁₁ versus E₃). Experimental results show that 90° domain switching is suppressed in the planes parallel to the compression direction. A domain-switching model dividing each 180° switching to two successive 90° switching was proposed to explain the experimental results.     

铁电陶瓷中电畴翻转研究进展

电畴为铁电陶瓷固有的独特微观组织特征之一,铁电陶瓷的许多性能均与其密切有关.综述了铁电陶瓷中的电畴结构,系统介绍了电场、机械作用引起的电畴翻转,概述了电畴翻转对铁电陶瓷断裂韧性的影响及其研究进展.     

Numerical analysis of ferroelectric/ferroelastic domain switching in ferroelectric ceramics

A numerical approach predicting the behavior of ferroelectric ceramics under electric field and mechanical loading is proposed in this paper. In the model, macroscopic properties of ferroelectric ceramics are determined by microscopic structures. Ferroelectric ceramics are seen to be composed of many domains with different orientations, and domain switching is the source of the nonlinear constitutive behavior of the ferroelectric ceramics. Numerical calculations based on the model were carried out, and the computational results are compared with the experimental results, which shows the two sets of results consist with each other. The calculation approach can provide a guidance for the ceramics component design.     

Nanoscale domain switching behaviour in polycrystalline ferroelectric thin films

We report on the nanoscale domain switching behaviour in polycrystalline tetragonal perovskite lead zirconate titanate (PZT) ferroelectric thin films investigated via piezoresponse force microscopy (PFM). Local domain structures were imaged as a function of varying biasing conditions and spatial location of the tip within 50-100?nm sized grains. Nanoscale piezoresponse images provided direct visual evidence of the complex interplay between electrical and mechanical fields in a polycrystalline system, which causes effects such as correlated switching between the grain of interest and neighbouring grains, ferroelastic domain switching, inhomogeneous piezostrain profiles and domain pinning on very minute length scales. Detailed investigations on mechanisms which induce such domain behaviour are presented.     

Variations in predicting domain switching of ferroelectric ceramics

In this article, a set of equivalent variational formulations for computing the driving forces for domain switching in ferroelectric materials is presented. It is proven that these formulations allow the free adoption of any couple of mechanical and electric fields as independent variables while obtaining consistent results. In addition, explicit expressions are provided for each formulation which allows for the study of the phase transformation process under different constraints.     

Self-consistent modelling of non-linear effective properties of polycrystalline ferroelectric ceramics

A constitutive model for the non-linear effective behaviour of ferroelectric ceramics is presented. The model is developed on the basis of the effective medium approximation (EMA), which describes the interaction of the crystallites in a statistical way. Additionally, a particular simplified domain configuration within the crystallites and the possibility of domain wall motion are taken into account. In connection with a thermodynamic criterion for the domain wall displacement the volume fractions of the domains can be calculated dependent on the crystallite orientation and the applied load in a self-consistent manner. This mechanism leads to an extrinsic contribution to the effective behaviour. If the domain wall displacement is associated with energy dissipation the macroscopic behaviour is non-linear and hysteretic.     

Effective electroelastic properties of polycrystalline ferroelectric ceramics predicted by a statistical model

Summary The effective electroelastic properties and moduli of ferroelectric ceramics are calculated. Based on a statistical model, the effects of the shape of individual domain and crystallographic domain switching under an external field are firstly taken into consideration to predict the effective electroelastic constants. The model's prediction of the effective electroelastic properties and moduli of a BaTiO₃ ceramic was found to be in agreement with the experimental results.     

Combined isotropic and kinematic hardening in phenomenological switching models for ferroelectric ceramics

A phenomenological model for ferroelectric switching is presented in this paper. The model is based on ideas of plasticity. A switching surface is used as the criterion for non-linear response of the material. Hardening models are used to control the size and position of the switching surface in electric field space. The distinctions between kinematic, isotropic and combined hardening models are discussed. The predicted response to electric loading is computed using combinations of isotropic and kinematic hardening. The calculated hysteresis loop and poling curve are in good agreement with experimental data.     

Effect of composition on rate dependence of ferroelastic/ferroelectric switching in perovskite ceramics

Abstract

The process of ferroelectric/ferroelastic switching is rate dependent as evidenced by the frequency dependence of the coercive field/stress in polarisation/strain–electric field/stress loops. The rate dependence of domain switching has been investigated in different compositions of ferroelectric/ferroelastic perovskites by studying their stress–strain hysteresis loops. Stress–strain loops were generated by applying a static compressive load and then superimposing cyclic compressive loads of different amplitudes and frequencies. The stress–strain loops were fitted using a Rayleigh type relationship, whose parameters characterise the intrinsic and extrinsic contributions to the strain. Using these parameters, the rate dependence of the extrinsic domain wall contribution was investigated.     

Preparation of polycrystalline BaTi2O5 ferroelectric ceramics

Polycrystalline BaTi₂O₅ (BT₂) was prepared by solid state sintering in air using BaCO₃ and TiO₂ as starting materials. A rod-like BT₂ sintered bodies in a single phase were obtained above 1025 °C by adding 5 wt.% B₂O₃. The densification of BT₂ sintered bodies decreased with increasing sintering temperature. The maximum permittivity of BT₂ sintered body was 640 at the Curie temperature (T_c) of 461 °C and the frequency of 100 kHz. The addition of B₂O₃ was effective to obtain BT₂ in a single phase at low temperatures with elongated microstructure and to improve the permittivity, indicating the formation of preferred orientation at low temperature was related with liquid-phase sintering mechanism.     

The influence of fabrication processing on domain structure and polarization switching in PZN-based ferroelectric ceramics

Lead zinc niobate (Pb(Zn_1/3Nb_2/3)O₃, PZN) based ceramics are prepared by using conventional mixing oxide and complex phase reaction-sintering ceramic techniques. From the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), it is clear that these two fabrication processing routes produce different microstructures and ferroelectric domains in the same Pb(Zn_1/3Nb_2/3)O₃–BaTiO₃–Pb(Zr_0.4Ti_0.6)O₃ composition. Furthermore, different phase transitions are observed for the temperature dependence of the dielectric permittivity that can be confirmed by differential scanning calorimetry (DSC). Different polarization switching characteristics are also examined by using high field-induced strain and ferroelectric hysteresis loop. It is suggested that the distribution of the inner stress and domain configuration should be related with the fabrication processing of ferroelectric ceramics.     

Memory switching in polycrystalline silicon films

Non-volatile memory switching has been observed in polycrystalline silicon layers produced by chemical vapor deposition. Evidence for filamentary conduction is found for devices which are in their low impedance state. Devices have been cycled through high and low impedance states up to a maximum of 2x10⁴ times. Exposure to transient ionizing electron radiation caused the devices to switch to their low impedance state.     

Strong ultrasonic microwaves in ferroelectric ceramics

It is well known that ferroelectric materials have piezoelectric properties which allow the transformation of electrical signals into mechanical signals and vice versa. The transducer action normally is restricted to frequencies up to the mechanical resonance frequency of the sample. There are, however, two mechanisms which allow transducer action in ferroelectric ceramics at much higher frequencies: one is the normal piezoelectric effect in a ferroelectric ceramic in which the crystallites have periodic domain structures, the other is a domain wall effect in which ferroelastic domain walls in a periodic domain structure are powerful shear wave emitters. Both mechanisms give rise to extensive dielectric losses in ceramics at microwave frequencies.     

Acoustic microscopy of ferroelectric ceramics

Ferroelectric ceramics have been observed in an acoustic microscope. The images demonstrate the ability of the microscope to image elastic properties and to penetrate opaque layers.