T h e guest species that has been successfully

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Unformatted text preview: echanism that drives the intercalation process is believed to be largely coulombic in nature ( 31). W hittingham ( 3 3 , 3 4) h as postulated that intercalation is a diffusion governed process and that in general, any species that is an electron donor could be intercalated into the layer compounds, and that there is some negative charge transfer from the intercalated species to the host layered compound. Kaluarachchi ( 32) u sed electron microscopy techniques to confirm that the guest species moves throughout the Van der Waals gaps of the host structure primarily by means of island motion. The movement of the Ag intercalation fronts in the Ag T i S s ystem was observed 2 x d irectly by optical methods and recorded on video tape. Upon intercalation, the guest species does not usually fill all the Van der Waals regions uniformly but instead exibits a phenomenon called "staging". Staging refers to the guest species intercalating only selected Van der Waals regions in the host structure in a n ordered sequence. The stage number " n " is the ratio of the number of successive Van der Waals regions divided by the number of regions containing the guest species, in an ordered sequence along the c-axis. For example, a "first stage" compound would have all successive Van der Waals regions occupied by the guest P age - 1 7 s pecies (Fig. 7) w hile an "n-stage" compound would have one of " n u s uccessive interlayer regions of the host structure occupied by the guest species (Fig. 8 , F ig 9 ). staging has been observed in K C 8 F ractional u sing elastic n eutron- s cattering ( 1 4 ) , w hereby a 3 /2 s tage compound would consist of 2 o ut of 3 s uccessive Van der Waals regions being occupied by t he intercalate species. Various attempts ( 58, 5 9 , 60) h ave been made to explain the process of staging by considering the coulomb interactions between the intercalate species and strain effects in the host lattice. Two of the models which attempt to explain the process of staging are the Classical model of staging and the Island model of staging ( 32). A ccording to the Classical model of staging the Van der Waals region...
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This note was uploaded on 10/08/2009 for the course CME MAT E 630 taught by Professor Dr. during the Fall '09 term at University of Alberta.

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