Sapphire Crystal Haze Cavity Formation And Annealing Grown by SAPMAC

Haze defect in SAPMAC method grown sapphire crystal was studied in detail. It is shown that haze is composed by a large number of CO2 bubbles, and haze always appears in the axis region of the crystal since the bubbles formed in front of the crystallization surface are most always draged to the convection rolls in front of the central part of the crystallizaiton surface by melt and then engulfed by the rolls. Moreover, the effects of pulling rate on the formation of haze were analyzed and means for restraining haze was suggested.

Shaped sapphire crystals were grown from the melt by the Stepanov (EFG) technique. High-temperature vacuum annealing of crystals grown in a reducing atmosphere, performed by employing graphite elements in the heater unit of the crystallization chamber, led to the formation of voids of two different types: (1) well-faceted voids which are the result of vacancy coagulation and (2) pores of irregular form which decorate the subgrain boundaries. The formation of these defects may be prevented by suppressing the interaction between the alumina melt and carbon.


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