Liquid alumina: detailed atomic coordination determined from neutron diffraction data using empirical potential structure refinement

The neutron scattering structure factor SN(e) for a 40 mg drop of molten alumina (Al(2)O(3)) held at 2500 K, using a laser-heated aerodynamic levitation furnace, is measured for the first time. A 1700 atom model of liquid alumina is generated from these data using the technique of empirical potential structural refinement. About 62% of the aluminum sites are 4-fold coordinated, matching the mostly triply coordinated oxygen sites, but some 24% of the aluminum sites are 5-fold coordinated. The octahedral aluminum sites found in crystalline alpha -Al(2)O(3) occur only at the 2% level in liquid alumina.