Effects Of The Application Of Electric Fields On The Growth Of Srb4o7 Crystals By The Micro-Pulling-Down Method

SrB4O7 (SBO) has received much attention as a solid-state ultraviolet laser crystal for a wide variety of applications such as micromachining and spectroscopy. Here we demonstrate the effects of electric fields E on the growth of SBO crystals along the b axis by the mu-pulling-down method to fabricate SBO with periodic twins, which increases the conversion light intensity. During the growth, the direction of electric fields was alternated for 30 min periods. The crystal fibers were evaluated by polarized optical microscopy, X-ray diffraction, and transmission electron microscopy. Without an external voltage, single SBO crystals grew. In contrast, at E >= 400 V/cm needles of SrB2O4 appeared inside SBO fibers. At E >= 1000 V/cm, new domains of SBO grew from the seed crystals, and interestingly, growth twins were formed perpendicular to growth fronts. Thus, we found that the growth of SBO by the mu-PD method via alternating the application of opposing electric fields exhibits two mechanisms. In contrast, when the electrodes in melt and growth fronts switched to + and -, respectively, growth fronts changed from concave into convex shapes, irrespective of E. We could explain the relation between the two mechanisms and the inversion of surface shapes, using the convection.