SYNCHROTRON X-RAY STUDY OF THE ELECTRON-DENSITY IN ALPHA-FE2O3

Structure factors for synthetic haematite, alpha-Fe2O3, have been measured for two small crystals using focused lambda = 0.7 angstrom synchrotron radiation. The structure factors from the two data sets are consistent. Approximate symmetry in the concordant densities, related more closely to the Fe-Fe geometry than to the nearest-neighbour Fe-O interactions, is similar to that in the corundum alpha-Al2O3 Structure. Deformation density maxima are located at the midpoint of the Fe-Fe vector along the c axis, on a common face for 0-octahedra, perpendicular to c. Maxima also occur at the midpoint of the Fe-Fe vector bisecting the edges of the 0-octahedra. These results are in accordance with theoretical predictions for metal-metal bonding. Space group R3cBAR, hexagonal, M(r) = 159.7, a = 5.0355 (5), c = 13.7471 (7) angstrom, V = 301.88 (7) angstrom3, Z = 6, D(x) = 5.270 MgM-3, mu0.7 = 13.68 mm-1, F(000) = 456, T = 293K, R = 0.019, wR = 0.021, S = 5.55 for 368 unique reflections in the most accurate data set 2.