TEM study of superstructure in a perovskite lead lanthanum zirconate stannate titanate ceramic

The superstructure of an antiferroelectric Pb0.97La0.02(Zr0.66Sn0.25Ti0.09)O-3 phase, whose composition is near the morphotropic-phase boundary, was characterized. Systematic selected-area diffraction revealed that there were two kinds of superlattice reflections in the pseudocubic reciprocal lattice, i.e. 1/2{hkl} superlattice reflections (h, k, l all odd), and g +/- 1/7.24(a* + b*) one-dimensional incommensurate superlattice reflections, where g denotes the vectors of fundamental or 1/2{hkl} supertattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of R (3) over barm. Based on the rhombohedral reciprocal lattice, the 1/2{hkl} reflections were no longer superlattice but fundamental reflections, and the reciprocal vector of the one-dimensional incommensurate reflections was re-expressed as H = ha* + kb* + lc* +/- 1/7.24(a* + b*), where h, k, l are integers and (-h + k + l) = 3n. In the light of the average structure and the reflection condition, the superspace Bravais class of the phase with one-dimensional incommensurate structure was determined to be P-11 (B (3) over barm) in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.