The ratio of the coarse grain region in the side wall in the thickness direction thereof is 10% or more and less than 90%. The coarse grain region is defined as such a region in which crystal grains having a grain size of 1 mm or more determined by an intercept method in the height direction of the crucible occupy 95% or more of an area of a measurement region, and the fine grain region is defined as such a region in which crystal grains having a grain size of 10 μm or more and 500 μm or less determined by the intercept method in the height direction of the crucible occupy 95% or more of the area of the measurement region.