Anomalous Diffractions in the Hull-Debye-Scherrer Spectrum of Graphite

Abstract

IN the course of an electron diffraction study of several graphites, Finch and Wilman¹ discovered a number of extra diffractions which could not be indexed in the normal way on the basis of the accepted crystal structure of graphite². Of the extra diffractions, two embracing the 1011 reflexion are clearly observed and cannot easily be accounted for. Because these extra lines occurred with graphites from very different sources, Finch and Wilman concluded that the possibility of impurity could be ruled out. Their main conclusion pointed to the presence of packets of planes with a thickness of 4 unit cells (or 9 layer-planes), in the direction of the c-axis. This would enable lines with fractional l indices to appear, because by analogy with a ruled grating with a few lines, the subsidiary maxima would begin to have the same order of magnitude as the principal diffractions. Thus the lines on either side of the 1011 would seem to be 101$\frac{2}{3}$ and 101 4/3;.