Observations of the decomposition of crystals of lead iodide in the electron microscope

Abstract

Abstract Thin crystals of lead iodide grown from solution have been examined in transmission in the electron microscope. The crystals are sufficiently stable in the electron beam to allow dislocations to be observed, but it is found that after prolonged periods of observation at high beam intensities decomposition commences, and proceeds through a number of stages to completion. The initial and intermediate stages are accompanied by the climb of pre-existing dislocations, the formation of new dislocations and the creation of other features which might be interpreted as cavities in the crystal. These can be understood to some extent as a result of the formation of vacancies in the crystal under irradiation with the electron beam. In the final stage the crystals appear to decompose completely leaving an aggregate of dense crystallites which are probably metallic lead. This is presumably accompanied by the release of iodine gas. The mechanism for this final stage of decomposition is not yet understood.