Multidimensional Disorder in Zeolite IM-18 Revealed by Combining Transmission Electron Microscopy and X-ray Powder Diffraction Analyses

A new medium-pore germanosilicate, denoted IM-18, with a three-dimensional 8 x 8 x 10-ring channel system, has been prepared hydrothermally using 4-dimethylaminopyridine as an organic structure-directing agent (OSDA). Due to the presence of stacking disorder, the structure elucidation of IM-18 was challenging, and a combination of different techniques, including electron diffraction, high-resolution transmission electron microscopy (HRTEM), and Rietveld refinement using synchrotron powder diffraction data, was necessary to elucidate the details of the structure and to understand the nature of the disorder. Rotation electron diffraction data were used to determine the average structure of IM-18, HRTEM images to characterize the stacking disorder, and Rietveld refinement to locate the Ge in the framework and the OSDA occluded in the channels.