ELECTRON-DIFFRACTION EVIDENCE FOR ORDERING OF INTERSTITIAL SILVER IONS IN SILVER BROMIDE MICROCRYSTALS

The occurrence and origin of diffuse intensity contours in electron mi crographs of AgBr crystals are investigated. The observations are inte rpreted in terms of a model, which attributes diffuse scattering to th e presence of predominant atom or vacancy clusters of a particular pol yhedral type. It is shown that irrespective of the crystal morphology, interstitial Ag ions order in AgBr material in clusters of finite siz e along 001 type planes. A different geometry of the diffuse intensity locus observed for triangular and hexagonal tabular grains is explain ed in terms of the different twin plane morphology of these grains.