Cation disorder in high dose, neutron-irradiated spinel

The crystal structures of MgAl2O4 spinel single crystals irradiated to high neutron fluences (>5x1026 n/m2 (En>0.1 MeV)), were examined by neutron diffraction. Crystal structure refinement of the highest dose sample indicated that the average scattering strength of the tetrahedral crystal sites decreased by similar 20% while increasing by similar 8% on octahedral sites. Since the neutron scattering length for Mg is considerably larger than for Al, this result is consistent with site exchange between Mg2+ ions on tetrahedral sites and Al3+ ions on octahedral sites. Least-squares refinements also indicated that, in all irradiated samples, at least 35% of Mg2+ and Al3+ ions in the crystal experienced disordering replacements. This cation sublattice disorder is the largest retained damage ever measured in an irradiated spinel material. ((orig.))