Diffuse X-ray scattering data were obtained for a crystal of wustite, Fe0.943O. Satellite reflections which corresponded to an incommensurate repeat distance of about 2.7a in all 3 cubic directions were observed (P’ phase). The satellites were diffuse, anisotropically elongated, interconnected by weaker continuous streaks, and were negligible in intensity beyond first order. Monte Carlo computer simulations demonstrated that this diffraction behavior was consistent with the presence of defect clusters which formed a paracrystalline (or highly distorted) lattice. The paracrystalline distribution which best fitted the observations was such that the spacing between defects tended to be maintained fairly constant, but relative lateral translations could be more variable. When these lateral translations were suppressed, additional superlattice peaks appeared which were consistent with the P’’-phase diffraction patterns. The diffuse satellites were more intense on the low-angle side of a Bragg reflection than on the high-angle side. This was explained in terms of the well-known atomic size effect, and was consistent with a local contraction of the structure around regions of low scattering power (defect clusters) and with a compensating expansion in other parts of the structure.

T.R.Welberry, A.G.Christy: Journal of Solid State Chemistry, 1995, 117[2], 398-406