Effect of Stacking Disorder on the Orientational Ordering Transition of Solid C ₆₀

We determine the nature of stacking disorder in C 60 by comparing x-ray powder diffraction patterns to simulated patterns of disordered crystals produced by a Monte Carlo method. Several samples have been specially prepared by rapid precipitation to have small grain size and significant stacking disorder. The diffraction patterns of these samples are well described by considering the density of one-dimensional disorder and the crystallite size. We give evidence and propose an explanation for the correlation found between stacking disorder and the appearance of new structure in the DSC endotherm of the C 60 orientational ordering transition, a phenomenon often observed for C 60 samples and not previously well understood.