The effect of platelet precipitates on the structure of lead sulphide films

Abstract

The authors are grateful to Miss D. Chescoe for assistance with the electron microscopy and to Mr. R. K. Taylor for his help in the numerical computation. It has been found that the interplanar spacings d(200) and d(220) for lead sulphide films, prepared on a rock salt substrate at 80°C, correspond to different values of a ₀ of 5·96 Å and 5·92 Å respectively (x-ray value 5·94 Å). A corresponding discrepancy has also been found in the ratio of the spacings of (200) and (220) moiré fringes formed between similar films of lead sulphide and lead selenide. Electron micrographs show the presence of platelet precipitates on {100} planes in the sulphide films. The expected atomic displacements around such platelets have been calculated and used to compute the diffraction pattern from such a distorted crystal. This calculation predicts an asymmetry of the same order as that observed experimentally.