X-ray diffraction from a 6H structure containing intrinsic faults

The theory of X-ray diffraction from a one-dimensionally disordered 6H structure (ABCACB) containing a random distribution of 14 unique intrinsic fault configurations has been developed. An exact expression for the diffracted intensity has been derived in terms of the coefficients of the characteristic equation and the boundary conditions by applying Holloway's method of analytic solution. This expression is then used to obtain the diffracted intensity in reciprocal space as a function of the 14 fault probabilities, assuming these to be small. Observable diffraction effects like peak broadening, peak shift and the change in the peak intensity are discussed for different single-crystal reflexions. A unique evaluation of all 14 fault probabilities is not possible from an experimental measurement of diffraction effects. However, it is often possible to neglect certain fault probabilities on the basis of physical considerations such as the stacking-fault energy and the mechanism of formation of faults in the 6H structure.