Ultra-pure oxide was prepared from multiply distilled Mg, and pure gaseous O2. Molecular beam epitaxy was used to prepare high-quality crystals with levels of trivalent cation impurities which had been reduced by a factor of about 100. By studying Ca and 18O tracer diffusion on the respective sub-lattices, it was deduced that the active impurity level during diffusion was a factor of 10 below that of high-quality commercial oxide. At temperatures where it was insensitive to the impurity content, the anion diffusion appeared to be consistent with theoretical predictions to the effect that anion jumps occurred mainly via the motion of bound vacancy pairs.

M.H.Yang, C.P.Flynn: Journal of Physics - Condensed Matter, 1996, 8[18], L279-83