Zeolites having various properties such as molecular adsorption, molecular sieves and solid-acids are widely used industrially as one of the major inorganic nanoporous materials. Powder X-ray diffraction is the most powerful structural analysis method because most porous materials can only be synthesized as polycrystalline powder. This article briefly describes some of our structural studies on novel zeolites, layered silicates, organic-inorganic hybrid porous materials determined by ab-initio structure analysis using powder X-ray diffraction data. In addition, improvement of the function of Rietveld analysis software was indispensable for the determination of these complex crystal structures. In the past development of multipurpose program RIETAN, we have incorporated many functions such as split-type profile functions, composite background function, MEM-based pattern fitting, and Le Bail method. This enables the highest level of pattern fitting for all angular dispersion powder diffraction patterns and enables efficient ab-initio structure analysis.
Dispersion corrected density functional theory （DFT） calculation is a powerful method for the refinement of crystal structures. This article presents a short introduction of computational methods and some examples of the refinements including the effects of the refinement on the calculated intermolecular interaction energies between neighboring molecules in crystals.
Atomistic structure defects such as impurity or vacancy could influence on materialsʼ properties, and therefore it is important to investigate the local atomic structures. However, chemical bonding state may be useful for the further understanding the relationship between the structure and the properties. Here, we show that atomic-resolution differential phase contrast imaging in scanning transmission electron microscopy is able to directly visualize the anisotropy of single Si atomic electric fields in monolayer graphene. Furthermore, we also investigate the atomic electric fields of Stone-Walse defects and nanoholes in graphene. Our findings open the way to directly examine the local chemistry at the structure defects in materials at atomic-scale.
Neutron and X-ray are complementary probes for structural study. Whereas X-ray is superior in terms of brilliance and resolution in general, neutron diffraction has better spatial resolution reflecting the difference in scattering medium; electron and nuclei for X-ray and neutron, respectively. This difference results in the fact that neutron diffraction has higher sensitivity to probe thermal vibration and off-center potential in a crystal. Here, as an example, I will show single crystal neutron diffraction study on ‘rattling’ in rare-earth based filled skutterudite compounds.