Growth and characterization of large stoichiometric magnesium aluminate spinel single crystals

Abstract

Large stoichiometric magnesium aluminate spinel single crystals with sizes up to one inch on an edge have been grown at 1250 °C by a flux method. Purification of the crystals from microscopic flux inclusions was obtained by a post-growth vacuum annealing process. The crystals were characterized by wet chemical analysis, X-ray and electron diffraction, optical microscopy, emission and mass spectroscopy. Information on composition, homogeneity, impurity content and lattice parameter was obtained. The crystals were examined by Lang X-ray topography. They exhibit dislocation densities as low as 50 lines/cm 2 and are of superior quality when compared to Verneuil and Czochralski melt-grown spinel crystals which were observed to have dislocation densities in excess of 10 5 and 10 3 lines/cm 2 respectively. Stacking faults with fault vectors R = 1/4 〈101〉 and randomly scattered small volumes of precipitates were observed in most of the crystals. Growth striations were found in some crystals. They are probably due to the segregation of impurities at the {111} solid-liquid interfaces during growth.