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

The superstructure of an antiferroelectric Pb0.97La0.02(Zr0.66Sn0.25Ti0.09)O3 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. 12hkl superlattice reflections (h, k, l all odd), and g±17.24a∗+b∗ one-dimensional incommensurate superlattice reflections, where g denotes the vectors of fundamental or 12hkl superlattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of R3m. Based on the rhombohedral reciprocal lattice, the 12hkl 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∗±17.24a∗+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 P11R3m in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed.