Various attempts 58 5 9 60 h ave been made to explain

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Unformatted text preview: s in the host crystal are either uniformly occupied by the guest species or are completely empty (Pig. 7 , F ig. 8 , F i g . 9). I n the classical model, the formation of higher stages from some initial stage compound involves either de-intercalation of the guest species with subsequent re-intercalation to form the higher stage compound or "tunnelling" of the guest species through the X - M - X h ost layers. The "de-intercalation, re-intercalation" process and the "tunneling" process both seem improbable in the formation of higher stages. The island or "Daumas and H erold" m odel of staging has the guest species occupying all successive Van der Waals P age - 18- r egions. In this model the guest species does not occupy the layer uniformly but instead forms islands within the layer ( F i g . 10). The periodicity of the islands along the c-axis of the crystal determines the stage of the compound. The higher stages may form simply by a re-arrangement of the islands of the intercalate species within the layers. Only two distinct stages have been observed in the A gxTiS2 s ystem as opposed to up to ten distinct stages reported (40) i n some of the intercalated graphite systems. The two stages reported ( 3 1 ) for Ag T i S x c orresponding to x ( x in the range x = = 2 w ere stage 2 m ole fraction of silver intercalate) 0 .15 - 0 . 2 5 and stage 1 f or x = 0 . 3 5 w ith mixed stage 1 a nd stage 2 co-existing for x 0 . 3 5 (45). = - 0 .42 0 .25 - S choltz and Frindt ( 31) h ave recently determined the structure of the stage 1 ( A g O a 4 T i S ) a nd stage 2 2 T iS ) c ompounds using X-ray diffraction with a D ebye (Ago.2 2 S cherrer camera. The silver atoms were found to reside predominantly in the octahedral sites ( 31) o f the interlayer region of the T i S 2 stage 2 c ompounds. h ost crystal in both the stage 1 a nd Scholtz (31) has plotted the variation i n l attice parameters of Ag T i S x 2 a s a function of various v alues of x f or both the stage 1 and stage 2 compounds, and thus the observed lattice...
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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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