Crystal chemistry of synthetic hercynite (FeAl₂O₄) from XRD structural refinements and Mossbauer spectroscopy

The crystal chemistry and thermal behaviour of synthetic hercynite a normal spinel, produced both hydrothermally and from sintering oxides at high temperatures, were studied by means of powder XRD and Mossbauer spectroscopy. The cation distribution shows a regular increase in disorder with temperature. The inversion parameter, x increases from 0.101(5) at 500°C to 0.187(4) at 900°C. The increase in x is accompanied by a similar smooth decrease of the oxygen positional parameter, u. Quenching of the intracrystalline disorder above 900°C was not possible. The thermal behaviour is anomalous compared to previously investigated simple oxide spinels. -from Authors