Diffraction peak shapes: a profile refinement method for badly resolved powder diagrams

Abstract

430SHORT COMMUNICATIONS course of our test experiments we changed the radius of curvature from R = 60 down to R = 20 m. The FWHM of the rocking curves varied in all cases within 10%.References ARROTT, A. S. & TEMPLETON, T. L. (1985). J. Appl. Cryst. 18, 388-395. KULDA, J. (1984). Acta Cryst. A40, 120-126. MIKULA, P., KULDA, J., HORALiK, L., CHALUPA, B. & LUKAg, P. (1986 AbstractA program has been specially written for biological powder spectra. Most existing programs are not suitable for such poorly resolved diagrams with broad bands in which individual peaks are not well separated. A more efficient version of the COMPLEX algorithm is used and this direct optimization method reduces the risk of false minima. Numerous internal parameters and options in the optimization algorithm as well as in the profile calculations lead to great flexibility. The performance and the limits of this version are tested by two applications on co-lactose monohydrate and native cellulose partial spectra. In the first case the results are excellent, according to values in the literature, and in the second case this program indicates some interesting features. This powerful algorithm can be used for more complicated refinements.

Water-induced crystalline transition of polyamide 66: a combined x-ray and molecular modeling approach

“…The part of the X-ray diffractogram ranging from 0 to 35 0 in 20 was refined with the decomposition method described by Tran and BulSon. 10 The position of each individual reflection was calculated, the peak shape being fitted with a Pearson VII type function. The refinement of the d spacings corresponding to the crystalline phases were performed using an optimization method based on a COMPLEX type procedure.11 Due to the low amount of experimental data, parameters were refined in two steps: first b, a, and y were refined while a, c, and 0, the parameters which define the hydrogen bonded sheet, were given their equilibrium values; second, a, c, and 0 were refined while the other data were kept fixed in their optimized values.…”