Analysis of time-resolved powder diffraction data using a pattern-decomposition method with restraints

Whilst the analysis of time-resolved powder diffraction data from simple high-symmetry crystals may be straightforward, the kinetic data from more complex materials such as molecular crystals can present a challenge. For such materials, the reflection density in the diffraction pattern tends to be high, giving rise to severe peak overlap between reflections of the different phases present. This problem can be further compounded by the poor spatial resolution inherent in time-resolved studies. Additional complications can arise owing to the use of a scanning detector in the dynamic studies. The latter can cause apparent variation of the relative integrated intensities of the reflections and introduce distortion into the diffraction pattern with respect to the 2θ axis. These complications, if present, rule out the use of currently available pattern-decomposition methods. In view of this, a new method has been developed. The method is based on the profile-fitting approach utilizing lattice parameters. The problems of peak overlap and correlation in the fitted intensities are overcome by restraints; the restraints attempt to maintain the relative integrated intensities of the reflections of each component (phase) in the mixed sample at the values observed for the pure component. The method is ideally suited to the analysis of time-resolved powder diffraction data and enables the reduction of data to a high precision.