Effects of temperature gradient on growth of SrB₄O₇ crystals by the micro-pulling-down method

Abstract

SrB 4 O 7 (SBO) shows superior transparency in the vacuum ultraviolet (UV) region, a high radiation damage threshold, and high nonlinearity, and SBO crystals have therefore attracted great interest as materials for low-cost, high-power UV light sources. To use SBO crystals as laser sources, it is essential to grow transparent SBO crystals. Here we show the effects of temperature gradient G on the growth of SBO crystals by the micro-pulling-down method. At low G, SBO crystal fibers were obtained. The density of striations and the size of voids also decreased with decreasing G. These results demonstrate that a low G is essential for growing completely transparent SBO crystal fibers. In addition, we considered the effects of G on the oscillatory growth of SBO crystals in relation to latent heat removal.

Effects of the Application of Electric Fields on the Growth of SrB4O7 Crystals by the Micro-Pulling-Down Method

“…Figure shows the hot zone of the μ-PD furnace. Electrodes were set in the μ-PD furnace used in our previous studies (Figure A). − A platinum crucible with a rectangular nozzle (5 mm × 1 mm × 2 mm (height)), which has a 0.4 mm cylindrical hole at the center of the base, was used (Figure B,C). To keep the temperature of the melt constant, the platinum crucible was surrounded by a refractory.…”

“…The stoichiometric composition was selected as the growth condition. These parameters were the optimized values in our previous studies to obtain high-quality SBO crystals. − During the growth, various voltages E in the range of 0–2000 V/cm were applied to growth fronts of seed crystals through Pt electrodes. Since the position of the Pt wire, which fixes the seed crystals, moves downward during the growth, the efficiency of the electric fields would decrease as the seed crystals are pulled down.…”

“…The temperature gradient range of the μ-PD method is 1–2 units larger than that of a general melt growth method such as the CZ method, since the hot zone is small. − When they are grown under a high-temperature gradient, SBO crystals with a homogeneous composition are made possible. We have in fact optimized the growth conditions and succeeded in obtaining transparent SBO single crystals. − The growth by the μ-PD method could be a suitable method for the uniform application of an electric field as well. We anticipate that, since the motion of molecules in a melt is faster than that in a solid, the alternating application of an electric field during the growth can control the orientation of the domains.…”

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

“…The µ-PD furnace used in this study was the same as in our previous studies [23][24][25][26]. Figure 1A-C show a hot zone of the µ-PD furnace.…”

“…Before the growth, the temperature profile from the bottom of the nozzle along the pulling-down direction was confirmed by a thermocouple. Then, the temperature gradient of 0.5-1 mm away from the nozzle was determined by the linear approximation [25]. These values would correspond to the intrinsic temperature gradient in the crystals near the interface to understand the crystal growth.…”