Hydrocalumite-type materials: 2. Local order into Ca2Fe(OH)6(CrO42−)0.5·nH2O in temperature studied by X-ray absorption and Mössbauer spectroscopies

Local order around the cations Fe3+ into Ca2Fe(OH)6(CrO42−)0.5·nH2O is studied by XAS and Mössbauer spectroscopies. The hydrocalumite phase Ca2Fe(OH)6(CrO42−)0.5·nH2O presents a Mössbauer spectrum which is refined with two distinct sites Fe3+, and two different distances Fe–Ca are necessary for the refinement of the XAS fine structure at Fe K edge.Upon calcination up to 250 °C where the inorganic phase turns amorphous, the cations Fe3+ is found to change from octahedrally to tetrahedrally coordinated. The corresponding isomeric shift (IS) is shifted from 0.35 to 0.2 mm/s, accompanied with an increase of the quadrupolar splitting. This is corroborated by a change observed on the absorption edge. Conversely, the local environment of the interlayered chromate oxoanions is unmodified in this range of temperature.