Magnetic Property and Crystal Chemistry of Ilmenite (MeTiO_3) and Hematite (αFe_2O_3) System : I. Crystal Chemistry

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Solid solutions of ilmenite (MgTiO_3, MnTiO_3, FeTiO_3, CoTiO_3 and NiTiO_3) and hematite (αFe_2O_3) were prepared and their crystal structure was investigated by an X-ray analysis. It was confirmed that the solid solutions could be classified into three groups: 1) The specimens of ilmenite side and hematite side in the solid solution have the different crystal symmetries; R3^^- and R3^^-c respectively and there exists a miscibility gap between them (MnTiO_3, MgTiO_3 and CoTiO_3 series). 2) Ilmenite and hematite make the solid solution in the whole range of composition and the crystal symmetry changes from R3^^- to R3^^-c continuously (NiTiO_3 series). 3) The ranges of the crystal symmetries R3^^- and R3^^-c of the solid solution are overlapped with each other and a transformation from R3^^- to R3^^-c is observed in one specimen of the overlapped range (FeTiO_3 series). Such differences among different ilmenite and hematite systems may be attributed to the following three factors; differences in ionic radii, in electronic conductivity and in stability of other two solid solution series with spinel and pseudobrookite structures which exist in a ternary system of MeO-Fe_2O_3-TiO_2.
1958-10-05