Growth of transparent SrB4O7 crystal fiber by the μ-PD method

We grew transparent SrB4O7 (SBO) crystal fibers by the micro-pulling-down (μ-PD) method at pulling rates (VP) of 0.01–0.40 mm/min. We observed the SBO crystals by optical microscopy. The SBO crystal fiber at VP of 0.40 mm/min was cloudy due to the incorporation of voids. In contrast, transparent single-crystal fibers were obtained at VP of less than 0.02 mm/min. This is the first time that transparent SBO crystal fibers have been grown with a length of several centimeters. These results demonstrate that it is crucial to grow SBO crystals at a low VP to obtain transparent crystal fibers. In addition, we considered the generation mechanism of voids in the SBO crystals by using the relation between the growth rate of SBO crystals and the diffusion rate of voids.