Structural reaction of PZT underin situconditions using synchrotron powder diffraction – influence and stability of nanostructures

Abstract

Keywords: ferroelectric oxids, in situ synchrotron xray powder diffraction, phase stability, nanodomains, Ferroelectric lead zirconate titanate, PbZr 1-x Ti x O 3 (PZT), is currently used in a wide range of applications converting electrical into mechanical energy. Highest strains and piezoelectric properties are found at the socalled morphotropic phase boundary (MPB) between tetragonal and rhombohedral symmetry. Previous results describe the structure at the MPB as monoclinic [1], whereas our recent studies using high-resolution synchrotron x-ray powder diffraction in combination with TEM and EPR [2,3] were able to correlate XRD observation with a nanodomain structure. The internal symmetry of the nanodomains is difficult to determine due to strong coherence effects in diffraction experiments, which is in correspondence with findings for relaxor ceramics using martensitic theory [4]. The stability field of these nanodomain structures is strongly dependent on sample composition, temperature and electric field. In situ synchrotron diffraction experiments in transmission mode at the beamline B2, Hasylab, Hamburg, reveal changes related to these three parameters. Furthermore, the microstructural reaction of the material is investigated under operating conditions. While the domain structure of samples with low nanodomain content is changed under electric field into that of the adjacent tetragonal or rhombohedral phase field, samples with a distinct balance between Zr-content and tetragonal c/a-ratio show stable nanodomains. These samples undergo reversible phase transitions between a mixture of tetragonal microdomains and nanodomains at the coercive field and rhombohedral microdomains at high voltage. In-situ electric field diffraction above the transition temperature between nanodomain structures and the tetragonal phase show tetragonal domain switching. Furthermore, temperature dependent measurements of the dielectric constant are able to clarify the character of the ferroelectric-to-paraelectric transition and gives new information on the behavior of nanodomain structures under field. This enables us to correlate properties of this material with the relaxor systems PMN-PT and PZN-PT.