抄録
Investigations of the phase relations in the quaternary system FeO-Fe2O3-P2O5-H2O under hydrothermal. conditions at 386° and 586°C and pressures of 0.3 GPa showed the existence of a solid solution between Fe2(PO4)O and Fe4(PO4)3(OH)3. The range of this solid solution extends between 0.18≤x≤0.60 according to a stoechiometry of Fe3+4-xFe2+3x(PO4)3(OH)3-3xO3x. The members of this series are isotypic to tetragonal β-Fe2(PO4)O (Spgr. I41/amd) and are therefore structurally related to the lazulite-type mineral phases. Rietveld analysis and 57Fe-Mössbauer spectra showed that the structure of these phases is characterised by an disordered distribution of Fe2+, Fe3+ and vacancies on the octahedrally coordinated Me-(8f)-sites giving rise to mixed valent Fe2.5+, Fe2.33+ and/or Fe2.66+ in finite clusters.
