The precipitation of lead during decomposition of lead iodide by electron irradiation

Abstract

Crystals of lead iodide decompose under electron irradiation into metallic lead and iodine gas. This paper describes the observations which have been made on the mode of decomposition, particularly on the way in which precipitates of lead nucleate and grow inside the parent crystal. At low rates of decomposition the lead precipitates almost uniformly in the form of very small (100 Å-1000 Å in diameter) misoriented crystallites. There is some slight tendency for deposition to occur along dislocations. At high rates of decomposition the lead precipitates in larger platelet form with a definite degree of orientation between the precipitates and the lead iodide. These platelets appear to nucleate and grow within cavities which are produced inside the parent crystal by the electron bombardment. The observations suggest an interesting mechanism for the growth and spreading of decomposition throughout the crystal.