Relaxor ferroelectric single crystals produce extraordinary strain levels in response to electric field, but the response is
highly dependent on temperature and bias stress. This behavior must be well characterized for the successful
development of actuation and sensor applications. This paper presents the results of experimental characterization of
<001> oriented single crystal PMN-xPT (<i>x</i> = 0.27 and 0.29) is presented for combined electrical and mechanical loading
at various temperatures. These data are contrasted with previously reported constitutive behavior of <001> single crystal
PMN-<i>x</i>PT with different compositions. The effects of composition on the phase transformation behavior and linear
material properties are compared and discussed.
Some relaxor ferroelectric single crystals undergo a diffuse phase transformation while others undergo a step like
transformation when driven by either stress or electric field. In this work the distributed transformation is modeled as a
sequence of distributed transformations associated with compositional fluctuations typical or relaxor ferroelectrics. The
distribution function is taken to be Gaussian. The results are in good agreement with observations of the response of
<011> cut PMN-0.32PT single crystals.
The behavior of ferroelectric ceramic materials is governed by complex multiscale phenomena. At the macroscale, the constitutive behavior displays time dependent coupling between stress, electric field and temperature. This behavior is dependent on composition, microstructure and dopants. Plasticity based macroscale phenomenological models utilize the concept of internal state variables and their evolution to represent the volume average behavior. These models include many variables that must be determined through a combination of experiment and micromechanical modeling. At the mesoscale, the microstructure plays an important role in the material behavior. Grains form during the sintering process and porosity can occur at grain boundaries. Upon cooling, the material undergoes a phase transformation to a ferroelectric state. Domains form within grains to minimize intergranular stress and electric fields. Within a single domain, the material behavior is governed by the crystal structure and the local fields. Micromechanics approaches connect the mesoscale with the macroscale. Micromechanical models utilize single crystal behavior and a self consistent approach to handling intergranular stress and electric fields to simulate the macroscopic behavior. This approach considers average local fields and utilizes volume fractions of domain types to characterize the state. This work implements measured single crystal behavior in a micromechanics code to predict the macroscopic material behavior. Specimens of the same composition are characterized under combined stress and electric field loading and the results are discussed.
Local fracture properties in poled [Pb(Zn<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>]<sub>(1-x)</sub>-[PbTiO<sub>3</sub>]<sub>x</sub> (x=0.045, PZN-4.5%PT) ferroelectric relaxor single crystals were assessed. The crystals were cut along the , , and  planes. Scanning electron micrographs of Vickers indentations for two different crack orientations were used to determine the crack tip toughness (K<sub>tip</sub>) and the local critical energy release rate (G<sub>tip</sub>). Cracks oriented along the  and  crystal planes were found to have practically identical local fracture properties. These properties were determined using Stroh's formalism to account for the large anisotropic material coefficients.