Defect structure of Fe_1-xO

Abstract

Short-range and long-range ordering of defects in Wüstite (Fe_1-xO), quenched from its stability field, have been studied using electron diffraction and high-resolution imaging in transmission electron microscopy. Defect clusters are observed, each containing more than seven net iron vacancies. Irregular ordering of these clusters in a pseudo-cubic superstructure (so-called P’ phase) generates diffuse diffraction maxima corresponding to an incommensurate superperiod 2.6–2.7 times the parameter a of rocksalt-structure FeO reference lattice. Commensurate ordering (P” phase) replaces the diffuse maxima with discrete superlattice reflections at (5a) ⁻¹ and generates a zig-zag arrangement of clusters. An analysis of superlattice reflection intensities and projected cluster images suggests 12:4 planar clusters (comprising four corner-sharing 4:1 complexes) arranged in a monoclinic supercell with C2 symmetry.