Structure of Precipated Cadmium Sulphide as studied by Single-Crystal Electron Diffraction Pattern

Abstract

CADMIUM sulphide crystallizes in two modifications : a cubic β-form (hawleyite¹ ; zinc blende-type) and a hexagonal α-form (greenockite ; wurtzite-type). According to Milligan², the former tends to be precipitated from cadmium nitrate (or sulphate) solutions and the latter from cadmium chloride (or bromide, iodide) solutions. Now, in the course of electron diffraction investigations of the action of a number of aqueous heavy metal salts upon a number of sulphide mineral surfaces³, cadmium sulphide in single-crystal orientation has been obtained on a cleavage face of galena (sodium chloride-type cubic ; cleavage, {001}) exposed to an acidic cadmium salt solution. The function of galena in this surface reaction is supposed to lie, first, in supplying sulphur ions to the solution by dissolving, leading to the precipitation of cadmium sulphide, and, secondly, in assigning an epitaxy to the precipitate without modifying its nature. Electron diffraction reflexion methods were used to discriminate between the two modifications of the precipitate. The results are summarized below.