2024, Vol.34, No.5

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

LiTaO₃ (Lithium Tantalate) single crystals are widely used in Surface Acoustic Wave (SAW) filters due to their excellent piezoelectric and optical properties. High-quality LiTaO₃ single crystals were preferably grown by czochralski methods for RF Saw filter applications. However, if the growth conditions are not optimized, internal cracks and defects which degrade piezoelectric performance tend to occur. To solve these problems, we should consider temperature gradient and thermal insulation to decrease thermal stress. In this study, an iridium cover was added above the iridium crucible to decrease temperature gradients and improve thermal insulation. The simulation results indicated that the temperature in the central region of the melt increased by up to 8.6K in the vertical direction and up to 6.4K in the radial direction. The addition of the iridium cover resulted in increases in both the maximum and minimum temperatures. In the vertical direction, the maximum temperature increased by 6.4K and the minimum temperature by 8.5K. In the horizontal direction, the maximum temperature increased by 2.6K, and the minimum temperature rose by 2.2K after applying the cover. The temperature gradient was also reduced with the addition of the iridium cover. The vertical temperature gradient decreased by approximately 39 %, while the radial temperature gradient decreased by 50 %. These results indicate that the iridium cover improves the thermal insulation and reduces the temperature gradient in the furnace.

Gallium, a key material in TFT (Thin-Film Transistor) targets and LED (Light Emitting Diode), is highly sought after due to its scarcity, making the recovering and recycling from waste resources. This study develops a process to recover high-purity gallium contained in an alkaline electrolyte and to produce gallium oxide nanopowder for IGZO (Indium Gallium Zinc Oxide) targets. Through an investigation of the electrowinning process conditions, the effects of various process factors and the optimal conditions are identified. It is found that the concentration of NaOH significantly affects purity. By employing two rounds of electrowinning followed by acid washing, gallium with a purity of over 99.995 % is successfully recovered. Using this recovered gallium as a starting material, gallium oxide is produced via a gas-phase synthesis. It is observed that while higher temperatures increase the yield, the purity decreases. Ultimately, at 1,260°C, gallium oxide nanopowder with a purity exceeding 99.995 % is obtained with a yield close to 90 %. The galliumoxide nanopowder predominantly exhibits a size of approximately 2μm and a spherical shape, suggesting favorable characteristics for subsequent processes such as sintering.

Silicon carbide (SiC), known for its excellent mechanical and chemical properties, is widely used in key industries such as aerospace, defense, and nuclear power generation. Due to its rapid heating characteristics when exposed to microwaves, SiC is being researched as a highly efficient heating element. In this study, Polycarbosilane (PCS) was treated by a mechanochemical reaction with iodine, followed by pyrolysis to create a microwave heating material. The effects of pyrolysis temperature and iodine additive content on microwave heating performance were investigated. The results showed that the fabricated specimen rapidly heated to a maximum of 800° C within approximately 60 sec and maintained a stable temperature of 700~750°C for up to 120 min