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When lead chloride is deposited onto substrates at temperatures below 150 K, a non-crystalline film is formed. This material crystallizes at temperatures above 260 K, as could be demonstrated by UV-VIS-spectroscopy. In order to determine whether or not the deposited material consists of extremely small crystals with a high degree of disorder or of a genuine amorphous phase, it was investigated by electron diffraction. We describe the procedure which we applied for the determination of the elastically scattered intensity as a function of the scattering vector. From this function, the reduced radial distribution function was determined. The results were compared with those reported about crystalline and molten lead chloride. The short range order in the cold condensed material is different from that in the crystal and that in the melt. Hence, cold condensation of lead chloride leads to the formation of an ionic glass.

By comparison of the UV spectra of freshly prepared cold condensed lead chloride films with those of tempered ones, it can be seen that initially non crystalline material is formed. The excitonic transitions give rise to broad structureless bands. Upon annealing, these bands shift and become more sharply. From the excitonic absorption at about 270 nm the non crystalline to crystalline transition can be monitored quantitatively. We can demonstrate that this is a first order phase transition. Nucleation is a necessary step. The initial non crystalline state therefore is metastable and not a frozen-in state.

By comparison of the UV spectra of freshly prepared cold condensed lead chloride films with those of tempered ones, it can be seen that initially non crystalline material is formed. The excitonic transitions give rise to broad structureless bands. Upon annealing, these bands shift and become more sharply. From the excitonic absorption at about 270 nm the non crystalline to crystalline transition can be monitored quantitatively. We can demonstrate that this is a first order phase transition. Nucleation is a necessary step. The initial non crystalline state therefore is metastable and not a frozen-in state.

UV/VIS spectroscopic studies with cold condensed silver chloride films are reported. During annealing of these films, an exciton band grows out of an initially contourless broad absorption edge. From the temperature dependence and from the time behavior of this absorption it is concluded, that the noncrystalline state of the chloride, which is formed during the condensation, is a metastable phase. The transition to the crystalline state is of an order > 1. A small red shift of the maximum of the exciton band during the transformation indicates that the crystalline nuclei grow during this process.