Study on crystal-melt interface shape of sapphire crystal growth by the KY method

•The effect of flow field structure and the change of crystal-melt interface shape were investigated during Kyropoulos process.•Shoulder concave and interface inversion are likely to take place due to the anticlockwise induced vortex formation at stagnation area in limited space with pressure gradient.•It helps to create a stable crystal-melt interface with larger temperature gradient and the interface shape is optimized by adjusting the powers.•The simulation results agree well with experimental observations in factory.

In this article, the influence of the flow field structure and temperature gradient of forefront interface on the shape of crystal-melt interface which may reflect the interface stability were analyzed through the method of numerical simulation by using CGSim software. In order to get a suitable interface shape and grow high-quality sapphire crystal, the heater arrangement should be adjusted during the KY process. The results indicate that the effect of Marangoni convection cannot be neglected at the last stage, the crystal-melt interface is governed by the flow field structure and the temperature gradient in melt at the crystal-melt interface. The phenomenon of shoulder concave appears at the stage of shoulder turning and interface inversion appears at the last stage during the crystal growth is discussed. Adjusting heater arrangement may effectively optimize the shape of crystal-melt interface.