HRTEM and Related Techniques

An early study of mica by HRTEM was reported by Buseck and lijima (1974). They clearly observed three dark lines representing a mica layer (the lines correspond to the two tetrahedral sheets and one octahedral sheet) and that cleavage was formed at the interlayer. During a quarter century after this pioneering work, many HRTEM studies for mica and related phyllosilicates have been reported (for instance, see the references in Baronnet 1992). These included many studies of mica, e.g., polytypism, transformations, defects and interface research. In the following section, recent HRTEM and related techniques are briefly reviewed. Next, two topics of HRTEM investigation, polytype and defect analyses are presented based on studies, mainly by the author and his colleagues. 

The Pt/LTL [. ], Pt/LTL [0.47, small], Pt/ASA and Pt/HT catalysts all have highly dispersed Pt particles. Based on the Htotai/Pt and Nptpt results, the average particle size for all these catalysts was estimated < 1 nm. The particle size for the Pt/ASA catalyst as revealed with HRTEM (1.5 nm) seems in contradiction with the other techniques. However, it has to be noted that with HRTEM the lower detection limit for Pt/ASA is approximately 8-10 A, and that on the HRTEM pictures taken only a small amount of particles was visible. In other words, with HRTEM the smallest particles, which make up the majority of all Pt in the Pt/ASA catalyst, are invisible. The relation between particle sizes as determined with HRTEM, H2 chemisorption and EXAFS was extensively described by de Graaf el a/35. 

General speaking, a crystal defect is a type of microstructure in which the parent crystal structure is locally disturbed. Such a microstructure carmot be described by a superstructure, even by an incommensurate superstructure. Since the defect areas are usually very small, they may not be detected by XRD and neutron diffraction methods. HRTEM is the most powerful technique to detect them and to investigate their relation with the parent crystals. The defects can greatly change the properties of an oxide. Some examples of the common defects in oxides are given in the following sub-sections. 

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