Epitaxial growth of magnesia and spinel on sapphire during incongruent reduction in molten magnesium

The types and structures of oxide phases produced during the incongruent re duction of sapphire (single-crystal Al2O3) by molten magnesium were examine d. Polished {<10(1)over bar 0>} faces of sapphire were exposed to molten ma gnesium at 1000 degrees C for 100 h. Such exposure resulted in the formatio n of a continuous, epitaxial layer of spinel (MgAl2O4) on sapphire and a co ntinuous, epitaxial layer of magnesia (MgO) on the spinel. X-ray pole figur e analyses indicated that two variants of spinel and magnesia had formed in a manner consistent with the following orientation relationships: (<10(1)o ver bar 0>)(Sapphire)\\(110)(Spinel)\\(110)(Magnesia)/[0001](Sapphire)\\[11 1](Spinel)\\[111](Magnesia).