Original paper

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

Larsson, Lena; O'neill, Hugh St.C.; Annersten, Hans

European Journal of Mineralogy Volume 6 Number 1 (1994), p. 39 - 52

25 references

published: Feb 4, 1994
manuscript accepted: Nov 3, 1993
manuscript received: Apr 9, 1993

DOI: 10.1127/ejm/6/1/0039

BibTeX file

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Abstract

Abstract The crystal chemistry and thermal behaviour of synthetic hercynite (FeAl2O4), a normal spinel, produced both hydrothermally and from sintering oxides at high temperatures, were studied by means of powder XRD and Mossbauer spectroscopy. The samples were annealed at different temperatures under controlled oxygen atmosphere in a gas mixture furnace using CO2/CO gas mixtures, and subsequently quenched. Both Rietveld refinement of the XRD powder pattern and Mossbauer spectroscopy were used to determine the cation distribution, which 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 as determined from XRD. From Mossbauer spectroscopy the figures are 0.162(8) and 0.19(1) respectively. 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. This may be explained by the extreme sensitivity of the defect chemistry of hercynite to variations in oxidation state, leading to the formation of ferric iron and vacancies in solid solution at elevated temperatures. This deviation from stoichiometry can be followed qualitatively by accurate lattice parameter measurements

Keywords

spinelhercyniteRietveld refinementMossbauer spectroscopycation distribution