Dislocation densities and crystallite size distributions in nanocrystalline ball-milled fluorides, MF2 (M = Ca, Sr, Ba and Cd), determined by X-ray diffraction line-profile analysis

摘要

The dislocation densities and crystallite size distributions in ball-milled fluorides, MF2 (M = Ca, Sr, Ba and Cd), of the fluorite structure type have been determined as a function of milling time by X-ray diffraction line-profile analysis. The treatment has been based on the concept of dislocation contrast to explain strain anisotropy by means of the modified Williamson-Hall and Warren-Averbach approaches and a whole-profile fitting method using physically based functions. In most cases, the measured and calculated patterns are in perfect agreement; however, in some specific cases, the first few measured profiles appear to be narrower than the calculated ones. This discrepancy is interpreted as the result of an interference effect similar to that described by Rafaja, Klemm, Schreiber, Knapp & Kuz. el [J. Appl. Cryst. (2004), 37, 613-620]. By taking into account and correcting for this interference effect, the microstructure of ball-milled fluorides is determined in terms of dislocation structure and size distributions of coherent domains. A weak coalescence of the crystallites is observed at longer milling periods. An incubation period in the evolution of microstrains is in correlation with the homologous temperatures of the fluorides.