CATION DISORDER IN HIGH-DOSE, NEUTRON-IRRADIATED SPINEL

The crystal structures of MgAl2O4 spinel single crystals irradiated to high neutron fluences (>5 X 10(26) n/m(2) (E(n) > 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 to 20% while increasing by similar to 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.