2 2 s cherrer camera the silver atoms were found to

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Unformatted text preview: parameters may be used as an indication of the degree of intercalation P age -18aFigure 10 Daumas and Herold Island model of s taging. Staae 1 S-Ti-S l ntercolote - S tage 2 s -Ti-s 4- I ntercalate Stage 3 P age - 1 9 - 2 - 3 (b) ~ n t e r c a l a t i d n M ethods The process o f i ntercalation is usually carried out by either electrochemical or thermal methods. Electrochemical intercalation o f t he dichalcogenides is u sually accomplished by immersing a d ichalcogenide cathode and a n a node made up of the intercalate in a suitable electrolyte then electrically connecting the cathode and anode. The mole fraction of intercalate which enters the host dichalcogenide can be continuously monitored by coulombic measurements as the intercalation process proceeds. The mole fraction of intercalate may also be determined by comparing the weight of the dichalcogenide cathode before and after intercalation or by quantitative X-ray fluorescence techniques (32). In the case of thermal intercalation, stoichiometric amounts of dichalcogenide powder and intercalate are placed inside evacuated ampoules and heated for some period of time. The intercalation of guest atoms generally causes an expansion in the host lattice perpendicular to the basal planes (typically 5 t o 10 p ercent) and a less dramatic expansion parallel to the planes (typically 1 t o 2 p ercent). 2-3 (c) Superlattice Formation Another phenomenon exhibited by the guest intercalate species upon intercalation is the formation of superlattice structures by the guest species within the host structure. P age - 20- T here are two aspects to the formation of an intercalate superlattice: i) intralayer ordering - t he ordering of the guest species between the X-M-X layers of the host crystal (within an intercalate layer). i i ) s tacking sequences - o rdering of the intercalate layers with respect to other intercalate layers with the intercalate occupying different in plane sites in different layers (eg. intercalate occupying a , b , c sites in successive intercalate layers). Parry e t . al. (40) o bserved intralayer ordering in graphite layered compounds intercalated with potassium, rubidium and cesium. Culik and Chung ( 36) m easured the...
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