Cation disorder and vacancy distribution in nonstoichiometric magnesium aluminate spinel, MgO•xAl2O3

Neutron diffractometry and X-ray diffractometry were used to characterize the cation disorder and vacancy distribution in nonstoichiometric spinel, MgO . xAl(2)O(3), where x greater than or equal to 1.0. Both synthetic and natural samples were examined. Least-squares refinements of integrated intensities for single crystals and Rietveld profile refinements for powders yielded the average scattering "power" from tetrahedral and octahedral sites within the almost-perfect cubic close-packed oxygen sublattice. The cation disorder was calculated assuming models in which the vacancies resided on tetrahedral, octahedral, or both types of sites. No degree of cation disorder was consistent with the tetrahedral vacancy model, and vacancies most likely resided on octahedral sites.