Effect of Dopants on the Defect Structure of Single‐Crystal Aluminum Oxide

Density and lattice parameter changes induced by dopants were studied in Czochralski rubies containing from 0.054 to 0.160 wt% Cr 2 O 3 , in Czochralski sapphires containing from 0.083 to 0.120 wt% TiO 2 , and in verneuil crystals grown from powders containing 250 to 1000 ppm Ca, Mg, Si, and V. Densities were determined within at least ∼0.005% using a hydrostatic weighing technique; lattice parameter shifts were measured within a maximum of 0.25% using a step‐scanning goniometer technique. Some crystals which appeared to be clear, transparent, and single‐phase contained fine particles of a second phase. It is concluded that Si 4+ and Ti 4+ ions enter solution with the formation of cation vacancies to maintain charge neutrality, that verneuil crystals contain vanadium as V 3+ , that the solid solubility of Ca 2+ is low (<340 ppm), and that MgO decomposes under verneuil growth conditions, resulting in formation of a second phase.