This preview shows page 1. Sign up to view the full content.
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
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...
View Full Document
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.
- Fall '09