Dynamic Simulation of the Temperature Field of LiH Single Crystal Growth

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 degrees C at 10 degrees C/min in a dual-temperature furnace and holding for 2.4 h. The crystallization margin was 46.5 degrees C after holding for 5 h. The crystallization margin of LiH at the cone point, respectively, decreased to 33.7 degrees C, 28.6 degrees C, 25.6 degrees C, and 16.5 degrees C when the upper furnace was maintained at 750 degrees C, and lower furnace was cooled to 680 degrees C, 650 degrees C, 630 degrees C, and 550 degrees C, respectively. The optimal conditions for obtaining large size and high-quality LiH single crystals were predicted to be 630 degrees 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 degrees with good chemical stability in air.