Utilizing vibration to promote microstructural homogeneity during floating-zone crystal growth processing

Abstract Mechanical vibration of amplitude in the range of 10–20 μm and frequency in the range of 1.0–1.5 kHz was applied during floating-zone processing to improve the homogeneity of NaNO 3 -18% wt% Ba(NO 3 ) 2 eutectics. Previously, it had been shown in a half-zone that controlled vibration induces a flow which streams away from the vibrating end wall along the zone surface, returning through the bulk. On superposing this controlled surface streaming on the thermocapillary convection (TC) in a float-zone, a quasi-stagnant region was observed in front of the growth interface. Temperature measurements in the zone under normal and vibrational growth conditions verify that vibration essentially eliminates radial temperature gradients ahead of the growth interface. Accordingly, the microstructural segregation is also eliminated. The radial uniformity of solidification structures and the observation of a flat interface shape during processing provide clear evidence for suppressing thermocapillary convection through vibration. By examining and comparing microstructures obtained from different growth conditions, it is further established that it is the temperature gradient change that promotes structural uniformity. These mechanisms and the influence of vibration parameters on the solidification structures are discussed.