Patent ID: 8016942

Claim:
A process for producing a metal fluoride single crystal using an apparatus for pulling a metal fluoride single crystal, wherein, in the apparatus, a double structured crucible constituted by an outer crucible and an inner crucible accommodated in the outer crucible is provided in a chamber forming a single crystal growth furnace, hollow portions of both the outer crucible and the inner crucible in the double structured crucible partially communicate with each other, the double structured crucible can continuously change an accommodating depth of the inner crucible with respect to the outer crucible, a single crystal pulling bar having a tip to which a seed crystal is attached so as to be used and suspended to be vertically movable is provided just above the hollow portion of the inner crucible in the chamber, and a circular opening portion for upward opening a gap space formed by an internal surface of the outer crucible and an external surface of the inner crucible is provided between an internal surface of a sidewall of the outer crucible and an external surface of a sidewall of the inner crucible; the process comprising: accommodating a raw metal fluoride melting solution in each of the hollow portions of the outer crucible and the inner crucible, and then, once reducing the accommodating depth of the inner crucible with respect to the outer crucible to cause the melting solution accommodated in the inner crucible to flow toward the outer crucible side; thereafter increasing the accommodating depth of the inner crucible with respect to the outer crucible again to feed, into the inner crucible, the melting solution in the outer crucible; and carrying out the operation at least once and subsequently starting an operation for pulling a metal fluoride single crystal.