Crystal Structure Analysis of Zeolites by Quantitative HRTEM Study

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We have applied a quantitative high-resolution transmission electron microscopy (HRTEM) technique to the structure analysis for several kinds of zeolite crystals and incorporated molecules inside micropores. First, we applied a slow-scan CCD camera attached to a 400kV HRTEM for improvement in the experimental resolution of contrast details in the synthetic zeolite structure MFI.The additionally resolved contrast features are shown to be due to the presence of organic TPA+(tetrapropylammonium) ions in the structural cage (Channels) of atomic framework of this material. The improvement in the amount and quality of strucutural detail through the use of the CCD camera is also shown by a comparison of a Fourier synthesis, made by using the observed electron diffraction intensities, with another one calculated by using a structure model based on X-ray measurements. The phases for both Fourier maps were calculated from the X-ray data. A comparison of the two Fourier calculations results in a good agreement, although the calculation of the diffraction intensities are based on the kinematical approximation. Rfactors based on the normalized diffraction intensities have also been employed to evaluate the results of the structure analysis. For more detailed structure analysis, we have evaluated an effect of dinamical scattering of electrons by the calculation using the framework structure of zeolite FAU,which is one of the best popular zeolite structure type having a low atomic packing density. The results of calculations indicated that the kinematical approximation can be applied up to the specimen thickness of about 30 nm, and is useful especially for the structure analysis of incorporated guest materials.