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

Abstract

The superstructure of an antiferroelectric Pb 0.97La 0.02(Zr 0.66Sn 0.25Ti 0.09)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 hk l 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 hk l superlattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of R 3m . Based on the rhombohedral reciprocal lattice, the 1 2 hk l 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) = 3 n. 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 R 3m in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed.