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W l and 'SF neutron activation analysis is used to determine the halogen content of synthetic P-FeOOH. Combined with 67Fe Mossbauer spectroscopy and TGA, new data are presented concerning the nature of the anion location and its role in the structure. A stoichiometrical model is proposed, allowing to obtain a more detailed knowledge of the content of interstitial water molecules in the compound.87Cl-und l0F-Neutronenaktivierungsanalyse wird benutzt, um den Halogengehalt von synthetischem p-FeOOH zu bestimmen. In Verbindung mit 67Fe-MoBbauerspektroskopie und TGA werden neue Daten zur Art der Anionenlokalisierung und ihre Rolle in der Struktur mitgeteilt. Ein stochiometrisches Model1 wird vorgeschlagen, das es gestattet, detailliertere Vorstellungen uber den Gehalt der Verbindung an Zwischengitterwassermolekulen zu erhalten. l) Proeftuinstrast 42, B-9000 Gent, Belgium.

The substitution of Ca2+ ions in magnetite is studied, mainly by Mössbauer spectroscopy. The Ca2+ ions are located at the tetrahedral sites and the conduction electrons can be described by a band model. The magnetite structure can at most contain 6.67 wt% of Ca. The presence of a Ca2+ ion at an A‐site decreases the hyperfine field at the neighbouring B‐site by about 30 kOe.

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