Precipitation in star sapphire III. Chemical effects accompanying precipitation

Publisher Website
Google Scholar
Abstract
Large prismatic dislocation loops, of interstitial character and with 1/3 〈1011〉 Burgers vectors are observed to lie on basal planes in the sapphire matrix around rutile needle precipitates in star sapphire. The loops climb away from the precipitate-matrix interface during ageing, and contain the material that has ‘plated out’ during precipitation. This plating out of material is necessary because the rutile lattice is less densely packed than that of sapphire. The area of these climbed-out loops depends on the nature of the charge-compensating defect that accompanies dissolution of aliovalent Ti4+ in sapphire; our results suggest that this defect is the oxygen interstitial rather than the aluminium vacancy.