A phase diagram for morphotropic ͑Pb 0.985 La 0.01 ͒͑Zr 1−x Ti x ͒O 3 is proposed based on a combination of X-ray and neutron powder diffraction experiments and complemented by transmission electron microscopy. Dependent on composition three regions are characterized. The stability range of tetragonal microdomains for high Ti contents, the stability range of rhombohedral microdomains for low Ti contents, and an intermediate stability range of nanodomains. All three regions exhibit a corresponding low temperature configuration. Temperature dependent diffraction revealed that lanthanum doping reduces the sensitivity of the structure to changes in temperature and composition. A continuous transition from pseudorhombohedral to tetragonal symmetry with an intermediate two-phase region at the morphotropic phase boundary is observed. A similar transition of low temperature superstructure phases from pseudorhombohedral to pseudotetragonal with an intermediate monoclinic phase governed by a continuous change in the oxygen octahedral tilt system from a − a − a − over a − a − c − to a 0 a 0 c − is identified.

domains in an isotropic arrangement. There are also other weaker patterns with axial symmetry about the Bragg rod. Application of a field brings about large changes. The diffuse scattering becomes much more diffuse, apparently involving a migration closer to the film Bragg peak, evidence of an increased spread in domain size and domain disorder. After removing the field the domain distribution does not relax back to the initial state, presumably reflecting the influence of domain wall pinning in stabilizing a field-induced domain geometry.

The symmetry of PbZr x Ti 1-x O 3 in the region of the morphotropic phase boundary is still under debate. Noheda et al. [1] claimed the existence of a monoclinic phase. In contrast to this Jin et al. [2] showed for relaxor ceramics that, if the width of tetragonal microdomains is smaller than the diffraction coherence length, the measured crystal lattice constants are of monoclinic symmetry. With convergent-beam electron diffraction (CBED) very small volumes can be examined. So crystal symmetry can be investigated on single domains. To distinguish the most probable phases with space group symmetry P4mm, R3m and Cm, just one zone-axis is needed. At most two projected CBED-patterns of neighbouring domains are necessary. The method will be explained by the use of simulated and experimental CBED-patterns.

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.

If the crystallites in a polycrystalline sample are oriented, the intensity of a reflection will vary as a function of the orientation of the sample in the X-ray beam. This means that even if two reflections overlap in a conventional powder diffraction pattern (i.e. have the same d-value), their intensities are likely to vary differently as a function of sample orientation, so their individual intensities can be deduced if data are collected at different sample orientations. It has been shown that this principle can indeed be exploited to obtain more single-crystal-like data from a polycrystalline material [1]. Although the initial study was performed in reflection mode, it was soon realized that a transmission geometry offered several advantages and the experiment was adapted accordingly. In particular, the problem of sample homogeneity was eliminated (the sample is bathed in the X-ray beam), the severe correction of the data for the sample tilt was no longer necessary, and less synchrotron beamtime was required. To start with, a 2-dimensional image plate detector was used, but the resolution of the diffraction patterns, both in d min (2θ range) and in peak width proved to be a limitation [2]. To overcome this, the experiment was changed once again to accommodate the 1-dimensional Mythen I Si-microstrip detector that was available on the Materials Science Beamline at SLS [3,4]. Now, a new version of this detector, Mythen II, has become available, and further optimization of the experiment can be undertaken. The detector now has a 2θ range of 120˚ (vs. 60˚), has a much larger dynamic range, and is not plagued by random dead and hot channels. Consequently, a different, more efficient, data collection strategy can be employed. Improvements in the data analysis software Maud [5] have also made it possible to reduce the data collection time. Constant 5˚ steps in the sample rotation (φ) and tilt (χ) angles are no longer required, so the number of sample orientations to be measured can be reduced from 1368 to 302 without sacrificing information content. The first measurements with the new detector and the new data collection strategy have now been performed. Textured samples of phlogopite mica and the aluminophosphate AlPO 4 -17 (ERI framework type), with known crystal structures, and of a niobium silicate with an unknown structure have been measured. Preliminary analysis of these data show that sensible orientation distribution functions can be derived, and the full intensity extractions are in progress. The crystal system of the niobium silicate was ambiguous because unit cells in several different crystal systems (hexagonal, orthorhombic, monoclinic) were possible. The texture analysis has now shown that only the orthorhombic unit cell is consistent with the measured pole figures.[1] Baerlocher, Ch.; McCusker, L.B.; Prokic, S.; Wessels, T. Z. Ferroelectric lead zirconate titanate solid solutions, PbZr 1-x Ti x O 3 (PZT), are frequently used in industrial applications exploiting the reaction of both the lattice and t...