Effects of the ferroelectric domain structure of PZT ceramics on powder diffraction

Abstract

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...