Morphology and formation mechanism of metallic inclusions in VB-grown sapphire crystals

Abstract

Morphologies of metallic inclusions observed in sapphire crystals grown by the vertical Bridgman (VB) technique using a tungsten (W) crucible were investigated. Square-or hexagonal-shaped inclusions 2 -5 m in size were observed in sapphire crystals around the interface between the seed and the grown crystal. It was found that such inclusions consisted of W metal used for the crucible. The morphology of some of the inclusions reflects a rhombic dodecahedron which is based on the cubic structure of W and is surrounded by {110} faces. It is probable that inclusions form in the sapphire melt during the crystal growth process, and then sink in the melt to the growth interface due to the high density of W.

Vertical Bridgman growth of sapphire—Seed crystal shapes and seeding characteristics

“…The development of the present method and techniques to the level of industrial technology is now in progress. The presence of some defects, such as voids, inclusions [16] and dislocations, and their characteristic distribution will be discussed in other papers.…”