Local structure of perovskite-based “Pb 2Fe 2O 5”

Abstract

The reciprocal lattice and defect structure of the crystallographic shear (CS) structures in perovskite-based “Pb 2Fe 2O 5” are investigated using transmission electron microscopy. The reciprocal space for all observed 1/2[110]( h0 l) p CS structures can be described with the same average pseudocubic unit cell with a ≈ a p ( a p – the parameter of the perovskite subcell), and modulation vector q ≈ α a ∗ + γ c ∗ with α/ γ ≈ h/ l and superspace group X2/ m( α0 γ) with a centering vector [1/2,1/2,1/2,1/2]. The defect structure is characterized by numerous mirror twins and coherent intergrowths of 1/2[110]( h0 l) p CS structures with different ( h0 l) p. There are no single CS planes in the perovskite matrix and there is no variation of the perovskite block thickness between the successive CS planes. The crystallographic similarity and the structural and chemical differences between the CS structures in “Pb 2Fe 2O 5” and those in ReO 3 and/or TiO 2-type oxides are discussed.