Deformations of the α-Fe2O3 rhombohedral lattice across the Néel temperature

High-resolution synchrotron radiation powder diffraction patterns of α-Fe2O3 measured between room temperature and 1100 K, i.e. above the Neel temperature TN = 950 K, have been analyzed. The integral breadths of the Bragg peaks show a hkl-dependent anisotropy, both below and above TN. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). J. Appl. Cryst. 32, 281]. Model calculations show that the rhombohedral α-Fe2O3 lattice is deformed and the deformation leads to a monoclinic lattice with the unique monoclinic axis along the hexagonal [110] direction both below and above TN. The monoclinic symmetry of bulk α-Fe2O3 is compatible with α-Fe2O3 nanowire growth along the [110] direction reported in Fu et al. [Chem. Phys. Lett. (2001), 350, 491].