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

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 3 and R 3 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 3 to R 3 c continuously (NiTiO 3 series). 3) The ranges of the crystal symmetries R 3 and R 3 c of the solid solution are overlapped with each other and a transformation from R 3 to R 3 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 .