Multiscale study of internal stress and texture in ferroelectrics

Recent developments in X-ray (synchrotron) and neutron diffraction facilities have offered a unique opportunity to study ferroelectric ceramics in situ at length scales ranging from sub-μm to cm. For the first time, material behavior in the sub-grain to bulk levels can be investigated under a wide range of conditions. Strain fields in BaTiO3: The local strain fields around domain walls in BaTiO3 were investigated for the first time using polychromatic scanning X-ray microdiffraction [1]. A tetragonal BaTiO3 single crystal was scanned with a sub-μm X-ray beam to determine orientation relationships across domain boundaries as well as the three-dimensional strain tensor associated with domains. The results suggest the presence of significant residual strain fields around domains. More recently, strain fields around cracks in single crystal BaTiO3 were also measured using the same technique. In another study, the in-situ response of individual grains in a polycrystalline BaTiO3 to electrical loading was studied using a high energy XRD method ("03-D XRD"). The latter data represent the constitutive behavior of BaTiO3 at the mesoscale. Constitutive behavior of Pb(Zr,Ti)03: In-situ uniaxial compression and electrical loading experiments were performed on various Pb(Zr,Ti)O3 or PZT ceramics using neutron and high energy X-ray diffraction. PZTs near the edge of the morphotropic phase boundary as well as single phase (tetragonal and rhombohedral) specimens were investigated. Analysis of the diffraction patterns allowed for observation of the onset and culmination of domain switching [2]. Elastic lattice strain data suggested a high degree of anisotropy and a complicated internal stress state. The results will be compared to the predictions of a new self-consistent model for ferroelectrics.