Catálogo de publicaciones - libros

Polarization switching is driven on the global scale by free energy reduction. The locally equivalent material force on a sharp domain wall can be expressed by Eshelby’s electromechanical energy momentum tensor. In the present paper, we deal with solids, which can be approximated by a linear response in the dissipation-free load range. In this case, the local driving force of dissipative transformations is represented by a particularly simple function of the jump of the linear material properties and of the electric field and mechanical stress on both sides of the domain wall (or before and after switching). Two generic examples for application are considered: (i) a numerical simulation of charge induced domain wall motions at a ferroelectric crystal surface; and (ii) a finite element homogenization procedure for ferroelectric or ferroelastic single domain switching in a volume element, which represents the macroscopic response of a material point.

In this investigation, the internal bias field in donor doped PZT ceramics was investigated through measuring both the electric hysteresis loops and the butterfly loops. The effects of both poling approaches and sieving methods on the internal bias field were examined. It was found that a sparse sieving technique, which leads to more defects and high porosity in PZT ceramics, may induce a larger internal bias field than a dense sieving one. Meanwhile, for the sparsely sieved PZT ceramics, a sample poled by an impact electric loading at room temperature has fairly good piezoelectricity and a negligible internal bias field, while a sample poled with field application above the Curie point or at 120°C has a considerably large internal bias field. Space charge concentration near the grain boundary defects and pores after poling is thought to be the cause of the distinct internal bias field.

In order to get some insight in processes leading to electric fatigue in piezoelectric materials, the interaction of point defects with domain walls is studied. The fundamental equations and quantities, relevant for the domain wall movement, are described within the framework of configurational forces. Using the Finite Element Method, numerical simulations have been accomplished for a number of typical defect domain wall configurations. The results are useful for understanding key features of the interaction. They indicate that a blocking of domain walls by agglomerated point defects actually seems to be possible and that this might be a dominant fatigue mechanism.

In-situ observation of electrically induced fatigue crack growth was carried out for ferroelectric single crystals under alternative electric field. Electrically-induced fatigue crack growth was observed both below and above the coercive field. The crack propagation behavior is a repeated process of a continuous increment followed by a sudden increase in the crack length. This jumped crack growth behavior was attributed to the variation of the crack boundary conditions under electric field cycling.

Crack initiation and crack propagation behavior was studied in a commercial soft PZT material under a cyclic electric field. A set of pertinent parameters that influence the crack propagation behavior was identified and their effect on the crack propagation behavior studied: the geometry of the notch, the viscosity of the surrounding liquid, the number of cycles and the electric field. To better understand the mechanism of crack initiation, linear piezoelectric FEM calculations were performed.

The coupled electromechanical behavior of a soft ferroelectric PZT53 under uniaxial, tension-torsion or compression-torsion loading has been investigated. By using plate type specimens and thin wall tube specimens, effect of uniaxial prestress in the poling direction and in the lateral direction (a direction perpendicular to the poling direction) on the electric and butterfly hysteresis response loops of PZT53 has been exploited. It is found that although both electric and butterfly hysteresis loops of PZT53 are sensitive to the pre-stress in the poling direction, the butterfly loops have additional sensitivity to the pre-stress in the lateral direction. Thin wall tube specimens are used to study the response of un-poled and poled PZT53 to proportional tension-torsion and compression-torsion loading. Initial ‘yield’ surfaces for un-poled and poled PZT53 are obtained.

Ferroelectric domain switching under low voltage or short pulses is of interest to the development of high-density random access memory (FRAM) devices. Being necessarily very small in size, instability and back switching often occurs when the external voltage is removed, and creates serious problems. In this investigation, a general approach to determine the minimum size of ferroelectric domain to avoid back switching was developed. As examples, two cases were considered in detail: one is a 180° domain in a ferroelectric thin film covered by the upper and lower electrodes, the other is a 180° domain in a ferroelectric thin film induced by AFM without the top electrode. We note that our approach is generally applicable to many other fields, including phase transformation, nucleation and expansion of dislocation loops in thin films.

A simple derivation of the body force produced by the applied electric field is given. The governing equations and boundary conditions on the problem of electrostriction with the correct constitutive equations and considering the pondermotive body force and boundary traction are obtained. Given also are the solution of first boundary problem for an infinite plate with an elliptic defect, and the asymptotic expansion of stress near the end of an elliptic defect. The stresses near the end of the major axis have the form of , but the principal part of the electric displacements have the form of if the origin of the local coordinate system is set at the focus point of the ellipse.

In this paper we study the effect of electric fields on fracture of functionally graded piezoelectric materials (FGPMs) via a perturbation-based complex variable method. To illustrate the new mathematical algorithm for the fracture analysis of FGPMs, we start with an anti-plane deformation of a cracked piezoelectric body with exponentially varying elastic properties in the direction parallel to the crack plane. First, we establish a perturbation-based complex variable method, which allows us to extend the available solutions for a homogeneous body to those for a nonhomogeneous body. Using the newly established method, we derive explicit expressions of field intensity factors for an impermeable crack and a permeable crack, respectively. Finally, we discuss the effect of electric fields on the fracture of FGPMs by applying the field intensity factors as a failure criterion. It is shown that the effect of electric fields on crack propagation in the FGPMs is qualitatively the same as that in a homogeneous piezoelectric material, i.e., the gradual variation of material does not change the propagation tendencies of cracks under an electric field.

In the charge-free zone (CFZ) model, dielectric and piezoelectric ceramics are treated to be mechanically brittle and electrically ductile. For an electrically conductive crack under electrical and/or mechanical loading, various charge emission mechanisms may function jointly at the tip due to the high electric field concentration. Charge emission and charge trapping consume more work and thus lead to a high value of the electric toughness. The failure criterions derived from the CFZ model were verified by experimental results on poled and thermally depoled lead zirconate titanate ceramics.