Full-pattern Refinement Research Articles

The combination of synchrotron powder diffraction and high-resolution solid-state NMR experiments

Structural investigations on three zeolites, ZSM-11, ZSM-12 and ZSM-5, have been carried out by a combination of high-resolution solid-state 29Si NMR experiments and Rietveld refinement of synchrotron X-ray powder data. These techniques, being sensitive to short- and long-range order, respectively, gave a most complete picture of the structure of the solid state. Variable temperature NMR experiments of ZSM-11 revealed a displacive phase transition with a change in symmetry at about 300 K. A Rietveld refinement of a data set recorded at 373 K confirmed the proposed structure model. The structure of ZSM-12 was refined from room temperature synchrotron powder data. Space group ambiguities because of psuedo-symmetry of the silica framework of the zeolite were resolved with the aid of 29Si NMR experiments leading to C2/ c as the true space group symmetry. 29Si NMR and X-ray studies of ZSM-5 showed that the symmetry of the crystal structure depends on the temperature, the concentration of the guest molecule, and on the number of Al atoms in the framework. A full pattern refinement of silica-ZSM-5 loaded with two molecules p-dichlorobenzene per unit cell showed that the site occupied by the sorbed molecule is not at the intersection of the channels but shifted by 1 4 along b 0.

X-ray diffraction study of disorder in Allied Spectra-1000 polyethylene fibers

Full-pattern refinement reveals a crystallite structure including disordered atoms that can be interpreted as indicating a wandering of the polymer chain from one ordered site to the next in the b-axis direction. Parameters of the model that were determined include the unit cells, disorientation, crystallite size and paracrystallinity, atomic coordinates, anisotropic temperature factors, the setting angle, and interactomic distances and angles