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A New Superstructure in Gamma-Ferric Oxide


SINCE 1935 it has been generally accepted that gamma-ferric oxide has the structure of magnetite (spinel structure) with cation vacancies1. The vacancies were assumed to be randomly distributed on all octahedral iron sites of magnetite. Magnetite contains 8 molecules of Fe3O4 in the face-centred cubic unit cell and has the space group Fd3m. Gamma-ferric oxide contains 10 2 3 molecules of Fe2O3 in the unit cell. Due to the occurrence of a number of extra reflexions in the X-ray diagram of gamma-ferric oxide also occurring in the diagram of ordered lithium ferrite Fe8[Li4Fe12]O32, and to the fact that the material he used contained some water, P. B. Braun2 of this Laboratory suggested that in these gamma-ferric oxide specimens the same superstructure occurs as in ordered lithium ferrite. The ideal composition for ordering would be Fe8[H4Fe12]O32. For compositions between Fe8[H4Fe12]O32 and Fe8[(Fe Fe 1 1 3 2 2 3 )Fe12]O32 the same superstructure reflexions were observed. (The square brackets [ ] denote the cations on octahedral sites, the ordinary brackets ( ) those on the Li-sites in ordered LiFe5O8.)

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  1. 1

    Verwey, E. J. W., Z. Krist., A, 91, 65 (1935). Hägg, G., Z. phys. Chem., B, 29, 88 (1935). Kordes, E., Z. Krist., A, 91, 193 (1935).

  2. 2

    Braun, P. B., Nature, 170, 1123 (1952).

  3. 3

    British Patent 688903.

  4. 4

    Collongues, R., thesis (Paris, 1957).

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