Synthesis And Characterization Of High Purity HgI₂ Poly-crystals

Mercuric iodide (HgI₂) crystal is one of the most potential compound semiconductor materials for room temperature nuclear radiation detector. High energy radiation detectors fabricated with this material are compact with small size and light weight, and can be widely used at room temperature for environmental monitoring, nuclear medical inspection, customs safety inspection, industrial non-destructive inspection, nuclear radiation detection, aerospace investigation, astronomy physics and high energy physics etc.The purities of the raw materials are very important to the growth of high quality HgI₂ single crystal, so the synthesis process of HgI₂ is vital. In order to obtain high-purity and optimum stoichiometry HgI₂ polycrystals, synthesis of HgI₂ from high-purity mercury (7N) and iodine (4N) was under taken by vapor phase reaction in double-temperature zone furnace based on the analysis of the synthesis principles of the Hg-I-HgI₂ system. The influence of iodine content ration and the temperature profile in the synthesis experiments was also discussed. The structure and the purity of the synthesized HgI₂ were analyzed by means of X-ray diffraction and inductively -coupled plasma/atomic emission spectrometer(ICP/AES). Scanning electronic microscope-energy dispersive X-ray analysis(SEM-EDX) and differential scanning calorimetry(DSC) were used to analyze stoichiometry concentrations and the phase transition of the polycrystals respectively. The obtained HgI₂ polycrystals was indexed to have a tetragonal α-HgI₂ structure with high-purity of 99.999% and good stoichiometry. The DSC test results show the phase transition temperature of HgI₂ is over 130℃ with a phenomenon of hysteresis. In addition, the analysis and calculation of the HgI₂ polycrystals phase transition kinetic are carried on.Through the both of experimental studies as well as theoretical analysis, anappropriate procedure for the synthesis of nigh quality Hgl2 polycrystailiiic materials as follows is obtained: (1) the starting materials should be introduced in an off-stoichiometry ratio with about wt.2.5% excess of I2;(2) the initial synthesis temperature of the reaction zone is started at 170"C and then elevated to 200 °C;(3) the temperature of condensing zone should be kept below 100°C.