Phase Relations in the System Fe2O3–Cr2O3–TiO2 between 1000 and 1300°C and the Stability of (Cr,Fe)2Tin−2O2n−1 Crystallographic Shear Structure Compounds

Abstract

Phase relations and the stability of crystallographic shear (CS) structure compounds (Cr,Fe)2Tin−2O2n−1 in the system Fe2O3–Cr2O3–TiO2 were investigated between 1000 and 1300°C. The ternary comprises five major solid solution series. These are as follows: an M2O3 series; an M3O5 series made up of two separate solid solution series—the first an orthorhombic pseudobrookite M3O5 solid solution and the second a monoclinic M3O5 series based on the V3O5 structure type; an M4O7 series; and an M5O9 series. These latter three series represent lower homologues (n=3, 4, and 5) of the (Cr,Fe)2Tin−2O2n−1CS compound series. Between adjacent M3O5 and M4O7 and M4O7 and M5O9 solid solutions, ordered intergrowths may occur. The stability and compositional limits of the solid solution series and intergrowth phases are dependent upon the temperature and Fe:Cr ratio. At high-TiO2 contents, assemblages may contain either members of the Andersson phase series Cr2Tin−2O2n−1, a continuous CS structure series extending into the ternary, or a rutile-based solid solution. A comparison of results from this study with previously published phase relations has led to a revised version of the Fe2O3–Cr2O3–TiO2 phase diagram.