Structural defects and their genesis in corundum monocrystals

✍ Scribed by E. R. Dobrovinskaya; Dr. L. A. Litvinov; V. V. Pishchik

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 348 KB
• Volume: 19
• Category: Article
• ISSN: 0232-1300
• DOI: 10.1002/crat.2170190216

✦ Synopsis

Structural Defects and their Genesis in Corundum Monocrystals

Besides the formation of dislocations and block boundaries behind the crystallization front, there is ~riuch experimental evidencv indicating the presence of rather big aggregates in various crystal-forming media. Experiniental facts are given proving them t o exist in A1,0, melt. The perfection of a grou n crystal depends on aggregation degree of the melt which can be controlled by both impurity cncentration and supercooling of the melt. E.g. in Verneuil-grown crystals a change in Cr concentration from 1 .

to 1% leads to a change in aggregate sizes from 100 t o 1000 A. With Stepanov-, Czochralski-, and horizontally directed crystallization methods a variation in supercooling the iiielt enables to change the size of the aggregates from 150 to 400 A. High values of the diffusion coefficient are accounted for by a higher concentration of the holes. The main reason increasing the number of holes in the crystals grown by the mentioned methods is the presence of the boundaries between incoherently accreted aggregates.