Precise Determination of Lattice Constants by Electron Diffraction and Variations in the Lattice Constants of Very Small Crystallites

Abstract

Previous workers have reported that lattice constants determined by electron diffraction differ from the accepted X-ray values. It has been suggested that these differences may be due to a change in lattice constant with crystal size. To examine this question further, the lattice constants of several alkali halides have been determined, by electron diffraction, to a higher accuracy than had previously been attained. The X-ray value of the lattice constant of TlCl was used as a standard reference. The lattice constants of six alkali halides, with crystal sizes greater than 150 A, were found to agree with the X-ray values to within the experimental error of 0.05% It has been shown that for crystal sizes less than 100 A the lattice constants of the alkali halides were found to be less than the X-ray values by an amount dependent on crystal size For a crystal size of about 30 A the decrease was approximately 0.5%