Growth Of PbI₂ Single Crystal By Top Seed Vertical Zone Melting Method

Lead Iodide(PbI2)single crystal is one of the promising materials for fabrication of room temperature nuclear radiation detectors,it has important application values in the field of scientific research,aerospace and the others.But PbI2 detectors have not been studied in detail because of the lack of high quality PbI2 single crystals.PbI2 is a kind of synthetic compound,its thermal decomposition products,Idodine and Lead,have a big difference in vapor pressure,which result in the difficulty for controlling the stoichiometry when growth PbI2 crystal by vapour method.The immiscibility of PbI2 melt also induces the deviation of stoichiometry when growth PbI2 single crystal by melt method.Based on the liquid-liquid phase segregation theory,this paper investigates the liquid-liquid phase segregation of PbI2 melt in crystal growth process and the syntectic reaction on the solid-liquid interface,explores the methods for supressing the coalescence of secondary droplets and enhancing the absorption of secondary droplets on the solid-liquid interface,and proposes the measurements for controlling the stoichiometry of crystal.Simutaneously this paper developes a new method for growth PbI2 single crystal,that is,top seed vertical zone melting method,which can generate many useful effects,such as impeing the melt decomposition,supressing the coalescence of lead-riched droplets,adjusting the syntectic reaction in order to control the stoichiometry PbI2 single crystal,as well as excluding the impurities and coagulated lead-riched droplets by using top-to-bottom zone melt method.The as grown PbI2 crystal with 15mm in diameter and 35mm in length is translucent,with orange red appearance and close to its stoichiometric,its resistivity is of 1012?·cm magnitude,infrared transmittance of more than 40%.It is sure that as grown PbI2 crystal lays a good experimental basis for the fabrication of PbI2 nuclear radiation detectors.