An electron-diffraction study of the transformation α-Fe2O3 to γ-Fe2O3

Finch, G. I. ; Sinha, K. P. (1957) An electron-diffraction study of the transformation α-Fe2O3 to γ-Fe2O3 Proceedings of the Royal Society of London - Series A: Mathematical and Physical Sciences, 241 (1224). pp. 1-8. ISSN 0080-4630

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Outgrowths formed on haematite single crystals by heating in air have been examined by electron diffraction. At 500°C a change occurs in their crystal structure, apparently due to the migration of some cations to tetrahedral interstices. Otherwise, the unit cell and oxygen-ion framework of this 'β-phase' remain as in α-Fe2O3 (haematite). At 700°C the structure of the outgrowths changes to one characteristic of γ-Fe2O3 and persists as such, even after prolonged heating at 900°C. Thus the transformation γ-Fe2O3 to α-Fe2O3 is not, as has been supposed, strictly irreversible, since the α-γ transition has now been found to occur under suitable conditions. The presence of β-phase traces seems to be the cause of the anomalous magnetic behaviour of haematite observed by Neel and others. It is concluded that the α-γ transformation is a necessary step preceding the solid-state spinelization reaction involved in the formation of a ferrospinel.

Item Type:Article
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