Evaluation of paracrystalline lattice distortion by profile analysis using a single X-ray diffraction peak

Abstract

A method of analyzing the paracrystalline lattice distortion and the size of crystallites was investigated by X-ray powder diffraction. This method was based on Fourier analysis of X-ray diffraction peaks and only a single peak was required for the analysis. The observed peak profiles were well described in split pseudo-Voigt function. After correction for the instrumental broadening, the Fourier coefficients for pure diffraction peak profiles were calculated. The size of the crystallites were calculated from the initial slope of the Fourier cosine coefficients at a harmonic number of 0; then the paracrystalline lattice distortion was evaluated from the extinction curve of the Fourier cosine coefficients. Crystalline powders of griseofulvin, tolbutamide and acetazolamide were used for the model drugs. In the griseofulvin powder, the paracrystalline lattice distortion increased and the size of the crystallites decreased with the grinding time. By the single-peak method, the paracrystalline lattice distortion was underestimated while the size of crystallites was overestimated, compared with those obtained by the multiple-peak method reported previously.