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

Abstract

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.