Dynamic Simulation of the Temperature Field of LiH Single Crystal Growth

Abstract

The single-crystal lithium hydride (LiH) generally grows in a gradient temperature region with the Bridgman method. A stable and appropriate temperature gradient is crucial in the crystallization process. In this paper, the temperature variation of single-crystal LiH growth is calculated by the finite element method (FEM). It is shown that the LiH compact melted entirely after heating to 750 °C at 10 °C/min in a dual-temperature furnace and holding for 2.4 h. The crystallization margin was 46.5 °C after holding for 5 h. The crystallization margin of LiH at the cone point, respectively, decreased to 33.7 °C, 28.6 °C, 25.6 °C, and 16.5 °C when the upper furnace was maintained at 750 °C, and lower furnace was cooled to 680 °C, 650 °C, 630 °C, and 550 °C, respectively. The optimal conditions for obtaining large size and high-quality LiH single crystals were predicted to be 630 °C at a lower-temperature-zone, 200 mL/min (cooling water flux), and 20 mm/h rise rate of the furnace. Based on the parameters of the above simulation, we synthesized LiH single crystal. X-ray diffraction (XRD) patterns showed that the LiH single crystal exhibited a (2 0 0) crystallographic plane at 44.5° with good chemical stability in air.

Thermal Field Simulation and Optimization of PbF2 Single Crystal Growth by the Bridgman Method

“…As the crucible continues to move in a vertical downward direction, the formed S-L interface and temperature distribution changes. In the areas with large temperature gradients, the melt can be driven to solidify to the crystal and simultaneously affects the temperature field distribution by releasing heat and changing the ratio of the melt/crystal existence [9][10][11]. Therefore, the conditions of the temperature field are one of the crucial conditions that ensures the normal growth of crystals in the actual crystal growth.…”

“…A.G. Ostrogorsky et al [21] obtained a convex S-L interface and excellent radial uniformity by designing a rotating immersed thermal insulation baffle. Yingwu Jiang et al [9] explored the effects of the low-temperature zone, cooling water, and furnace rise rate on the temperature field of a LiH single crystal grown through the VB method. In general, the stable and suitable temperature fields and S-L interface have crucial roles in the growth of high-quality crystals.…”