An Application of Calculated X-Ray Diffraction Patterns in the Analysis of Reference Powder Data: Trivalent Metal Sulfates

Abstract Powder diffraction patterns have been calculated for nine isostructural rhombohedral M 2 (SO 4 ) 3 (M = Sc, Ti, V, Cr, Fe, Ga, Y, Rh, In) phases, and for four isostructural monoclinic M 2 (SO 4 ) 3 (M = V, Fe, In, Tl) phases. The pattern for monoclinic Fe 2 (SO 4 ) 3 is the first reported for this phase. Because structure data are available only for the two Fe 2 (SO 4 ) 3 polymorphs, the powder patterns of the other trivalent metal sulfates were approximated using the structure data of the isostructural Fe phases with the scattering factors and previously determined cell parameters of the various metal sulfates. These calculated patterns are termed an approximation by isostruduralism . The calculated patterns were used to evaluate reference powder data for these phases in the Powder Diffraction File (PDF). All but two of the PDF patterns were found to differ substantially from the calculated patterns in the stronger peaks used for identification, and to be missing weak peaks that may be confused for impurities during phase identification.