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Author

Stephen C. Hwang

Other affiliations: Forschungszentrum Jülich
Bio: Stephen C. Hwang is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Ferroelectricity & Electric field. The author has an hindex of 11, co-authored 13 publications receiving 1260 citations. Previous affiliations of Stephen C. Hwang include Forschungszentrum Jülich.

Papers
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Journal ArticleDOI
TL;DR: In this article, lead lanthanum zirconate titanate (PLZT) was loaded with compressive stress parallel to the polarization and the stress vs strain curve was recorded.
Abstract: Ferroelectric and ferroelastic switching cause ferroelectric ceramics to depolarize and deform when subjected to excessive electric field or stress. Switching is the source of the classic butterfly shaped strain vs electric field curves and the corresponding electric displacement vs electric field loops [1]. It is also the source of a stress—strain curve with linear elastic behavior at low stress, non-linear switching strain at intermediate stress, and linear elastic behavior at high stress [2, 3]. In this work, ceramic lead lanthanum zirconate titanate (PLZT) is polarized by loading with a strong electric field. The resulting strain and polarization hysteresis loops are recorded. The polarized sample is then loaded with compressive stress parallel to the polarization and the stress vs strain curve is recorded. The experimental results are modeled with a computer simulation of the ceramic microstructure. The polarization and strain for an individual grain are predicted from the imposed electric field and stress through a Preisach hysteresis model. The response of the bulk ceramic to applied loads is predicted by averaging the response of individual grains that are considered to be statistically random in orientation. The observed strain and electric displacement hysteresis loops and the nonlinear stress—strain curve for the polycrystalline ceramic are reproduced by the simulation.

651 citations

Journal ArticleDOI
TL;DR: In this paper, a polarization switching model for polycrystalline ferroelectric ceramics was developed, in which a single ferro-electric crystallite in a ceramic, which is subjected to an electric field and/or a stress, undergoes a complete polarization change and a corresponding strain change if the resulting reduction in potential energy exceeds a critical value per unit volume of switching material.
Abstract: A polarization switching model for polycrystalline ferroelectric ceramics has been developed. It is assumed that a single ferroelectric crystallite in a ceramic, which is subjected to an electric field and/or a stress, undergoes a complete polarization change and a corresponding strain change if the resulting reduction in potential energy exceeds a critical value per unit volume of switching material. The crystallite’s switch causes a change in the interaction of its field and stress with the surrounding crystallites, which is modeled by the Eshelby inclusion method to provide a mean field estimate of the effect. Thus the model accounts for the effects of the mean electric and stress fields arising from the constraints presented by surrounding crystallites as well as the externally applied mechanical and electrical loads. The switching response of the ceramic polycrystal is obtained by averaging over the behavior of a large number of randomly oriented crystallites. The model, along with the linear dielect...

191 citations

Journal ArticleDOI
TL;DR: In this article, a finite element model of switching in polycrystalline ferroelastic ceramics is developed, where the reduction in mechanically driven potential energy of the system exceeds a critical value per unit volume of switching material.

115 citations

Journal ArticleDOI
TL;DR: In this article, a finite element model of polarization switching in polycrystalline ferroelectric ceramics is developed, which involves electric field induced switching and strain effects are neglected.
Abstract: A finite element model of polarization switching in polycrystalline ferroelectric ceramics is developed. A polarization switch in a ferroelectric is the reorientation of the unit cell dipole to a new crystallographic direction. It is assumed that a crystallite switches if the reduction in potential energy of the polycrystal exceeds a critical energy barrier per unit volume of switching material. The crystallite's transformation causes a disruption of the local field which is computed by the finite element method. Each crystallite is represented by a finite element with the possible dipole directions assigned randomly subject to crystallographic constraints. The model involves electric field induced (i.e., ferroelectric) switching and strain effects are neglected. Different values for the energy barrier to the switch are selected to model the electric displacement versus electric field hysteresis loop of a ceramic lead lanthanum zirconate titanate (PLZT) at room temperature and a best fit is obtained.

92 citations

Journal ArticleDOI
TL;DR: In this article, the potential energy of an infinite homogeneous piezoelectric loaded body containinga single ellipsoidal transforming inhomogeneity is stated in terms of the fields in the inclusion.
Abstract: The potential energy of an infinite homogeneous piezoelectric loaded body containinga single ellipsoidal transforming inhomogeneity is stated in terms of the fields in the inclusion. Explicit results are given for a piezoelectric inclusion in an isotropic matrix having the same elasticities and dielectric permittivity as the inclusion. The results are used to construct criteria for the first crystallite to switch in an unpolarized polycrystalline ferroelectric.

77 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the impact factors on the hysteresis loops are discussed based on recent developments in ferroelectric and related materials, including the effect of materials (grain size and grain boundary, phase and phase boundary, doping, anisotropy, thickness), aging, and measurement conditions (applied field amplitude, fatigue, frequency, temperature, stress), which can affect the hysteretic behaviors of the ferroelectrics.
Abstract: Due to the nature of domains, ferroics, including ferromagnetic, ferroelectric, and ferroelastic materials, exhibit hysteresis phenomena with respect to external driving fields (magnetic field, electric field, or stress). In principle, every ferroic material has its own hysteresis loop, like a fingerprint, which contains information related to its properties and structures. For ferroelectrics, many characteristic parameters, such as coercive field, spontaneous, and remnant polarizations can be directly extracted from the hysteresis loops. Furthermore, many impact factors, including the effect of materials (grain size and grain boundary, phase and phase boundary, doping, anisotropy, thickness), aging (with and without poling), and measurement conditions (applied field amplitude, fatigue, frequency, temperature, stress), can affect the hysteretic behaviors of the ferroelectrics. In this feature article, we will first give the background of the ferroic materials and multiferroics, with an emphasis on ferroelectrics. Then it is followed by an introduction of the characterizing techniques for the loops, including the polarization–electric field loops and strain–electric field curves. A caution is made to avoid misinterpretation of the loops due to the existence of conductivity. Based on their morphologic features, the hysteresis loops are categorized to four groups and the corresponding material usages are introduced. The impact factors on the hysteresis loops are discussed based on recent developments in ferroelectric and related materials. It is suggested that decoding the fingerprint of loops in ferroelectrics is feasible and the comprehension of the material properties and structures through the hysteresis loops is established.

869 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of experimental evidence and present understanding of nonlinear dielectric, elastic and piezoelectric relationships in PEG ceramics.
Abstract: The paper presents an overview of experimental evidence and present understanding of nonlinear dielectric, elastic and piezoelectric relationships in piezoelectric ceramics. This topic has gained an increasing recognition in recent years due to the use of such materials under extreme operating conditions, for example in electromechanical actuators and high power acoustic transducers. Linear behaviour is generally confined to relatively low levels of applied electric field and stress, under which the dielectric, elastic and piezoelectric relationships are described well by the standard piezoelectric constitutive equations. Nonlinear relationships are observed above certain ‘threshold’ values of electric field strength and mechanical stress, giving rise to field and stress-dependent dielectric (e), elastic (s) and piezoelectric (d) coefficients. Eventually, strong hysteresis and saturation become evident above the coercive field/stress due to ferroelectric/ferroelastic domain switching. The thermodynamic method provides one approach to describing nonlinear behaviour in the ‘intermediate’ field region, prior to large scale domain switching, by extending the piezoelectric constitutive equations to include nonlinear terms. However, this method seems to fail in its prediction of the amplitude and phase of high frequency harmonic components in the field-induced polarisation and strain waveforms, which arise directly from the nonlinear dielectric and piezoelectric relationships. A better fit to experimental data is given by the empirical Rayleigh relations, which were first developed to describe nonlinear behaviour in soft magnetic materials. This approach also provides an indication of the origins of nonlinearity in piezoelectric ceramics, in terms of ferroelectric domain wall translation (at intermediate field/stress levels) and domain switching (at high field/stress levels). The analogy with magnetic behaviour is also reflected in the use of Preisach-type models, which have been successfully employed to describe the hysteretic path-dependent strain-field relationships in piezoelectric actuators. The relative merits and limitations of the different modelling methods are compared and possible areas of application are identified.

447 citations

BookDOI
01 Dec 2008
TL;DR: In this article, the authors presented a detailed analysis of Piezoelectric Transducers for Sonar Applications. And they proposed a method to construct a three-dimensional piezelectric fiber composite material for medical transducers, which can be used for medical diagnosis and NDE.
Abstract: Fundamentals of Piezoelectricity- Thermodynamics of Ferroelectricity- Piezoelectricity and Crystal Symmetry- Crystal Chemistry of Piezoelectric Materials- Piezoelectric and Acoustic Materials for Transducer Technology- Lead-Based Piezoelectric Materials- KNN-Based Piezoelectric Ceramics- Bismuth-based Piezoelectric Ceramics- Electropolymers for Mechatronics and Artificial Muscles- Low-Attenuation Acoustic Silicone Lens for Medical Ultrasonic Array Probes- Carbon-Fiber Composite Materials for Medical Transducers- Transducer Design and Principles- Piezoelectric Transducer Design for Medical Diagnosis and NDE- Piezoelectric Transducer Designs for Sonar Applications- Finite Element Analysis of Piezoelectric Transducers- Piezoelectric Transducer Fabrication Methods- Piezoelectric Fiber Composite Fabrication- Composition Gradient Actuators- Robocasting of Three-Dimensional Piezoelectric Structures- Micropositioning- Piezoelectric Actuator Designs- Piezoelectric Energy Harvesting using Bulk Transducers- Piezocomposite Ultrasonic Transducers for High-Frequency Wire Bonding of Semiconductor Packages- Piezoelectric MEMS: Materials and Devices- High-Frequency Ultrasonic Transducers and Arrays- Micromachined Ultrasonic Transducers

421 citations

Journal ArticleDOI
TL;DR: In this paper, a constitutive model for the non-linear switching of ferroelectric polycrystals under a combination of mechanical stress and electric field is developed for nonlinear switching, where the switching event, which converts one crystal variant into another, gives rise to a progressive change in remanent strain and polarisation.
Abstract: A constitutive model is developed for the non-linear switching of ferroelectric polycrystals under a combination of mechanical stress and electric field. It is envisaged that the polycrystal consists of a set of bonded crystals and that each crystal comprises a set of distinct crystal variants. Within each crystal the switching event, which converts one crystal variant into another, gives rise to a progressive change in remanent strain and polarisation and to a change in the average linear electromechanical properties. It is further assumed that switching is resisted by the dissipative motion of domain walls. The constitutive model for the progressive switching of each crystal draws upon elastic–plastic crystal plasticity theory, and a prescription is given for the tangent moduli of the crystal, for any assumed set of potentially active transformation systems. A self-consistent analysis is used to estimate the macroscopic response of tetragonal crystals (representative of lead titanate) under a variety of loading paths. Also, the evolution of the switching surface in stress-electric field space is calculated. Many of the qualitative features of ferroelectric switching, such as butterfly hysteresis loops, are predicted by the analysis.

388 citations