HIGH-PURITY LEAD IODIDE FOR CRYSTAL-GROWTH AND ITS CHARACTERIZATION

High purity lead iodide (PbI2) is prepared by precipitation of lead nitrate (Pb(NO3)) and potassium iodide (KI) solutions. Thoroughly dried PbI2 is then zone refined. The main impurity causing a strong adherence of solidified melt to the glass ampoule wall is identified to be lead-hydroxyl-iodate (Pb(OH)I). In order to decrease the OH- concentration and consequently the deviation from stoichiometry, molten PbI2 is treated with a gaseous mixture of methylene-iodide (CH2I2) and iodethane (C2H5I). The criterion for the efficiency of this scavenging process is the removal of the adhesive effect; thus, the solidified PbI2 ingot can move freely in the ampoule. A wet chemical analytic method to determine the deviations from stoichiometry is described.