Monoclinic deformation of the crystal lattice of hematite α-Fe2O3

Lineshape analysis of high resolution synchrotron radiation diffraction patterns of polycrystalline α-Fe2O3 powders show distortions from trigonal (space group R-3c) symmetry. The symmetry lowering is observed for α-Fe2O3 polycrystalline powders from several commercial vendors. The experimental observations can be explained by assuming a monoclinic symmetry (space group C2/c). The relative differences between the monoclinic and the hexagonal lattice constants are of the order of 10−4. The monoclinic symmetry of the crystal structure of α-Fe2O3 (C2/c) is in agreement with magnetic space group analysis [American Mineralogist 95 (2010) 974].