A study of the growth mechanism of bismuth silicon oxide during LHPG method

Single-crystal fibers of Bi₁₂SiO₂₀ were grown by a laser-heated pedestal growth (LHPG) method. The thermal radiative emissions during the growth were monitored by a thermal imaging radiometer with a 5 μm bandpass filter. The variation in thermal emissions in the 5 μm spectrum during the growth process reflects the interior structure of re-crystallized Bi₁₂SiO₂₀. When a crystal fiber was grown upward from a sintered powder rod, bubbles oscillate in the upper floating zone and may be caught within the grown crystal, which may cause the inclusions, color fragments, voids or other defects inside the grown crystal. When we grew a crystal downward to minimize the effects of the bubbles, the defects were reduced, but could still be observed inside the crystal. In order to solve this problem, we used a two-pass method that is during the first pass, we grew downward to obtain an almost bubble-free polycrystalline rod. In the second pass, we grew the single-crystal fiber upward using the polycrystal source rod obtained in the first pass. The grown fiber has uniform luster and higher transmissivity.