Structural disorder in microcrystalline MgCl 2

Structural disorder in severely ground MgCl 2 is interpreted on the basis of a Bernoullian model with four parameters, specifying both the size and the statistical sequence of the layers; their choice completely dictates the intrinsic shape of all the X‐ray diffraction lines. The X‐ray powder spectra are reasonably well reproduced over a wide range of Bragg distances (~1.7 < d < ~9 Å) for samples with various degrees of disorder. Practical criteria are given to derive the statistical parameters from the X‐ray spectra. Average crystal thickness as small as 20 Å across the layers is observed. From the usual structure with cubic packing in the Cl atoms, with increasing disorder at first the probabilities of cubic and hexagonal‐like interlayer shifts ( P cub and P hex ) tend to become equal; the ultimate degree of disorder also involves ± 60° rotations between adjacent layers, with about the same probability as P cub and P hex .