 The crystallization rate depends on the temperature gradient above the shaper, which is determined by the configuration of the hot-zone of the crystal growth furnace, and the power applied to the heating elements during growth.The difference in thermal expansion coefficients between the shaper material and the crystal material can also cause appreciable size differences between the shaper and the crystal at room temperature for crystals grown at high temperatures.The shaper material should be non-reactive with both the melt and growth atmosphere, and should be wet by the melt.