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

Structure factors for synthetic haematite, alpha-Fe2O3, have been meas ured for two small crystals using focused lambda = 0.7 angstrom synchr otron radiation. The structure factors from the two data sets are cons istent. Approximate symmetry in the concordant densities, related more closely to the Fe-Fe geometry than to the nearest-neighbour Fe-O inte ractions, is similar to that in the corundum alpha-Al2O3 Structure. De formation density maxima are located at the midpoint of the Fe-Fe vect or along the c axis, on a common face for 0-octahedra, perpendicular t o c. Maxima also occur at the midpoint of the Fe-Fe vector bisecting t he edges of the 0-octahedra. These results are in accordance with theo retical predictions for metal-metal bonding. Space group R3cBAR, hexag onal, 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 refl ections in the most accurate data set 2.