Magnetic Property and Crystal Chemistry of Ilmenite (MeTiO3) and Hematite (αFe2O3) System I. Crystal Chemistry

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Abstract
Solid solutions of ilmenite (MgTiO 3 , MnTiO 3 , FeTiO 3 , CoTiO 3 and NiTiO 3 ) and hematite (αFe 2 O 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; R \bar3 and R \bar3 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 R \bar3 to R \bar3 c continuously (NiTiO 3 series). 3) The ranges of the crystal symmetries R \bar3 and R \bar3 c of the solid solution are overlapped with each other and a transformation from R \bar3 to R \bar3 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 2 O 3 ·TiO 2 .