Patent ID: 7785416

Claim:
A crucible for growth of a single crystal along the crystal plane of a seed by melting and cooling an optical part material, comprising a starting material carrying section in which the starting material of said optical part material is loaded and a seed carrying section in which said seed is loaded, a tapered cone surface formed between the starting material carrying section and the seed carrying section, a concave curved plane surface formed at a border section between the starting material carrying section and the tapered cone surface, and a convex curved plane surface formed at a border section between the tapered cone surface and the seed carrying section, wherein a cone angle of the tapered cone surface formed between the starting material carrying section and the seed carrying section is set in a range between 95° and 150°, and wherein curvature radii of the concave curved plane surface and the convex curved plane surface are at least 1/10 of an inner diameter of the starting material carrying section.