A New Technique for the Production of Synthetic Corundum

LARGE crystals of corundum have been grown for many years by the flame-fusion process originated by Verneuil 1 . Crystals coloured by small amounts of chromium, titanium, vanadium and other transition metal oxides are used in the gem industry and as jewel bearings and gramophone styli. The recent interest in ruby (chromium-doped corundum) as a paramagnetic material for use in masers and lasers has directed attention to the imperfections of the flame-fusion crystals. In particular, the inhomogeneity of chromium distribution in the crystals, the excessive residual strain and gross lattice imperfections detract from their usefulness in micro-wave and optical devices. Alternative methods of growth capable of giving better quality crystals are therefore of considerable interest for research in solid-state physics.