A study of the vacancy distribution in non-stoichiometric spinels by magic-angle spinning NMR

A series of spinels of the general form MgO·xAl2O3 (x = 1·00 to x = 3·40) have been examined by magic-angle spinning (MAS) NMR to determine the vacancy distribution. It is found that the non-stoichiometric vacancies introduced with increasing x occupy the octahedral interstitial cation sites, rather than being randomly distributed or occupying tetrahedral sites. This study demonstrates that MAS-NMR can provide a convenient, readily interpretable method for examining structural problems in solids. A comparison is made with the earlier X-ray studies of the problem.