The effects of growth parameters on bubble formation in Al2O3 crystals in the Czochralski method were inves tigated. Pure Al2O3 single crystals were bubble free both under non-reducing and reducing atmospheres. Ti doped Al2O3 single crystals grown under a H2-contain ing atmosphere were bubble free and those grown un der non-reducing atmospheres contained many bub bles. The effective segregation coefficient of Ti ions was estimated to be greatly reduced under non-reduc ing atmospheres.

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... of the melt was remarka bly enhanced under a H2-containing atmosphere. The conditions for the bubble formation is concluded to be similar to that of constitutional supercooling.