Neutron diffractometry and X-ray diffractometry were used to characterize cation disorder and vacancy distributions in the non-stoichiometric spinel, MgO-xAl2O3, where x was greater than 1. Synthetic and natural samples were examined. Least-squares refinements of the integrated intensities for single crystals, and Rietveld profile refinements for powders, yielded the so-called average scattering powers of tetrahedral and octahedral sites within the almost-perfect cubic close-packed O sub-lattice. The cation disorder was calculated by assuming that the vacancies were situated on tetrahedral, octahedra or both types of site. No degree of cation disorder was consistent with the tetrahedral vacancy model, and the vacancies were expected to reside most probably at octahedral sites.

Cation Disorder and Vacancy Distribution in Nonstoichiometric Magnesium Aluminate Spinel, MgO-Al2O3. R.I.Sheldon, T.Hartmann, K.E.Sickafus, A.Ibarra, B.L.Scott, D.N.Argyriou, A.C.Larson, R.B.Von Dreele, 1999, 82[12], 3293-8