STUDY OF THE LOCAL STRUCTURE IN POORLY-ORDERED PRECURSORS OF IRON OXI-HYDROXIDES

X-ray absorption spectroscopy has been used to study the local structure of poorly-ordered ferric hydroxides. Materials obtained by oxidation of divalent iron and by precipitation from trivalent iron solutions present the same oxygen environment around iron atoms, but different from that of crystalline compounds. Fe-nearest Fe distances indicate that adjacent octahedra share edges. Local structures of both materials can whereas be distinguish because of their different iron atomic shells. During its transformation into hematite (alpha-Fe2O3) the evolution of the local structure of the material precipitated from ferric solution has been followed: the dehydration induces a shortening of Fe-Fe distances and the distortion of octahedra.