Exploring New Approach To Synthesis And Melt Growth Of Hg₂I₂Crystal

Mercurous Iodide (Hg2I2) single crystal is a kind of important acousto-optic material, its transmission range is0.5～40u m covering that of a large number of acousto-optic crystal. it has important application value in scientific research, military and other fields, but has not been applied as the lack of excellent single crystal. Hg2I2decompose easily when heated. Because of the large vapor pressure difference between mercury and mercury iodide, it is difficult to control the stoichiometry of Hg2I2crystal in the vapor transport growth process. Hg2I2is insoluble in solvents as sulfuric acid, nitric acid, ethanol, diethyl ether. In the presence of water, Hg2I2decomposes into mercury iodide and mercury, so it is difficult to obtain Hg2I2single crystal by solvent method. Hg2I2is a kind of syntectic compound, above the synthetic reaction temperature, immiscible melt layers can be observed clearly. When growth Hg2I2single crystal with melt method, immiscible layer makes it impossible to get Hg2I2crystal by melt condensation directly.In this paper, iodine and mercury elementary substance are used as raw materials, zone heating vapor transport and liquid phase synthesis method are used to obtain mercurous iodide. Based on the liquid-liquid phase separation theory and combined with PbI2single crystal growth method, this paper observed the mercurous iodide melt condensation process, analyzed the phenomenon such as decompression boiling, immiscible melt layers, condensing crystallization in the cooling process thoroughly, put forward a new method for synthesis Hg2I2polycrystalline materials—melt standing-fast cooling-standing. A three layers raw rod is obtained with this method. In this raw rod, the upper layer is eutectic of mercury iodide and mercurous iodide, the middle is mercurous iodide and the lower is mercury, mercurous iodide polycrystalline materials close to the ideal stoichiometry can be obtained after removing the upper and the lower layers. On the basis of these preliminary work, vertical zone melting experiment with the row material ingot was carried out, mercurous iodide ingot has loose and porous structure when the zone melting temperature below synthetic reaction temperature and has compact structure when above it. It shows that mercurous iodide single crystal can be grown by vertical zone melt method above the synthetic reaction temperature. In addition, after analyzing the growth process of density mercurous iodide polycrystalline ingot, it is suggested that mercurous iodide is crystallized from melt, which laid the theory and experiment foundation to product quality mercurous iodide single crystal.