Control of growth interface shape using vibroconvective stirring applied to vertical Bridgman growth

The ability of vibroconvective stirring to control the growth interface shape during vertical Bridgman growth was demonstrated using the coupled vibrational stirring (CVS) technique. CVS involves the application of low-frequency vibrations to the outside of the growth ampoule and produces strong flows emanating from the fluid surface. Previous studies showed that the growth rate and interface shape fluctuations occurred under growth with a constant vibrational frequency. In order to eliminate these fluctuations, this paper examines methods to lower the vibrational frequency as growth progressed to maintain a constant fluid flow rate in the vicinity of the growth interface. These flow control methods were tested on two growth systems: NaNO3 and lead magnesium niobate-lead titanate (PMNT). The previously observed fluctuations were greatly reduced when flows were appropriately controlled. Using this control method, CVS flows were then applied to reduce the concavity of the growth interface in the NaNO3 system at fast growth rates (>10 mm/h).