Layer Diameter in Graphite

Abstract

THE X-ray method of estimating the layer diameter in samples of graphite, based on the breadths of the hk0 reflexions, leads to apparent diameters of a few hundred Å, On the other hand, electron micrographs of the same sample show flakes the dimensions of which are some thousands of Å, nearly an order of magnitude larger. The discrepancy could arise from the simultaneous occurrence of strain broadening and particle-size broadening, or from the ‘tangent-plane approximation’^1,2 being insufficiently good. The only hk0 reflexion which can readily be examined is 11&2macr;0, and measurements of integral breadths or half-widths require two reflexions in order to separate strain broadening and particle-size broadening. Measurement of the variance of a line profile, on the other hand, can in principle separate the two effects even when only one line is available for examination³. Use of the variance also makes it possible to allow for some departure from the conditions within which the tangent-plane approximation is valid.