STRUCTURAL-ANALYSIS OF THE TRANSFORMATION MECHANISMS IN IRON-OXIDES AND OXYHYDROXIDES

A simple representation to describe structures of oxides built up from close-packed stackings (in particular for iron oxides) is developed by referring to the concept of plane trigonal lattices discussed previously by a number of workers. The formalism presented here is used to simply describe topotactic transformations and reactions such as the gamma-->alpha transformation of Fe2O3 and the synthesis of iron oxyhydroxides as well as transformation mechanism. These mechanisms rely on displacements of Shockley partial dislocations inside the close-packed structures concerned. Finally, a mathematical operator is put forward which, when applied to the lacunar spinel structure of gamma-Fe2O3, describes the gamma-->alpha transformation of iron sesquioxide.