Deformations of the $α$-Fe$\sb 2$O$\sb 3$ rhombohedral lattice across the N\'eel temperature

High-resolution synchrotron radiation powder diffraction patterns of $α$-Fe$\sb 2$O$\sb 3$ measured between room temperature and 1100K, \it i.e. above the N\'eel temperature \it T$\sb N$ = 950K, have been analyzed. The integral breadths of the Bragg peaks show a \it hkl-dependent anisotropy, both below and above \it T$\sb N$. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). \it J. Appl. Cryst. \bf 32, 281]. Model calculations show that the rhombohedral $α$-Fe$\sb 2$O$\sb 3$ 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 \it T$\sb N$. The monoclinic symmetry of bulk $α$-Fe$\sb 2$O$\sb 3$ is compatible with $α$-Fe$\sb 2$O$\sb 3$ nanowire growth along the [110] direction reported in Fu \it et al. [\it Chem. Phys. Lett. (2001), \bf 350, 491].