Structural Analysis of Poor Crystalline Ferrite Precursor, γ-FeOOH, Derived from Topotactic Hydrolysis of FeOCl

Abstract
Layered compound FeOC1 has iso-stucture with γ-FeOOH, which is considered as precursor of various magnetic materials in wet chemical synthesis. γ-FeOOHcan be prepared by topotactic hydrolysis of FeOCl under a severe reaction condition (60°C, 2 weeks). But the samples are often very poor in crystallinity under such a condition, so that the diffraction method can hardly be applicable. XAS spectroscopic studies at the Fe K-edge have been performed for FeOCl and its oxide/hydroxide derivatives. By comparison of XANES spectra for between γ-FeOOH and reference compounds such as FeOCl, Fe₂O₃, and Fe₃O₄, it is confirmed that the iron octahedron becomes centrosymmetric as the chlorine atom was replaced with (OH). Detailed structure including bond angle as well as bond distance was obtained from Fe K-edge EXAFS analyses combined with powder X-ray diffraction for γ-FeOOH over long range up to 6 Å which is very large value in case conventional EXAFS curve-fitting.