Growth of SrB4O7 Crystal Fibers along the c-Axis by Micro-Pulling-Down Method

Abstract

SrB4O7 (SBO) receives much attention as solid-state ultraviolet lasers for micro-machining, photochemical synthesis, and laser spectroscopy. For the application of SBO, the SBO crystals require the control of twinning to amplify the conversion light. We also expected that the inhibitation of the SrB2O4 appearance was essential. Here, we show the growth of SBO crystals along the c-axis through the micro-pulling-down method while alternating the application of electric fields (E). Without the application, single crystals were grown. At E ≧ 400 V/cm no needle domains of SrB2O4 inside SBO crystals existed; however, composition planes were formed and twin boundaries did not appear. In contrast, the inversion of surface morphology emerged, and the convex size was especially large at 1000 V/cm. These results demonstrate that convection is generated perpendicular to the growth front by alternating the application of electric fields. This surface morphological change contradicts the conventional concept of growth through the micro-pulling-down method. The distance from seed crystals vs. grain density plot also showed that the density did not decrease with a sufficient slope. Consequently, we concluded that the selection of the c-axis as growth faces is not fruitful to fabricate twins, and the selection of the growth condition, under which geometrical selection strongly affects, is the key.