The variance and other measures of line broadening in powder diffractometry. II. Determination of particle size

The procedure for interpreting broadened diffraction maxima in terms of particle size is illustrated by means of two samples of nickel powder. The average size of the particles in submicron nickel is determined from a comparison of various measures of breadth of broadened profiles with the breadths of `standard' lines. Information about the shape of the particles and an indication of the distribution of size are also obtained. The size from X-ray methods (about 200 Å) is in close agreement with the value obtained from electron micrographs of the powder, indicating that the grains observed in the latter are mainly single crystals. The limitations of this technique are discussed for cases in which diffraction broadening is not appreciable. An advantage of the variance as a measure of breadth is that it provides a direct method of investigating crystal imperfections. Data from a sample of carbonyl nickel powder, with an average grain size of 5.5 μm, are used to illustrate this method. The mean particle size is 650 Å, indicating that each grain consists of several coherently diffracting regions, or 'particles' as determined by X-ray methods.