1 t he six fold coordination of the chalcogenide

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Unformatted text preview: al properties being very anisotropic and the anisotropy is enhanced by intercalation. For example, Silbernagel et. al. (48) found that expansion of the T iS 2 l attice parameters parallel to the a axis is an order of m agnitude less than the expansion parallel to the c axis when lithium is added t o the host T iS2 c rystal. M oSZ i s the only transition metal dichalcogenide that occurs naturally in appreciable quantities but the other transition metal dichalcogenides may be easily g r o w n , usually b y c hemical vapor transport methods (27). , A m ore complete description of . P age -8aF igure 1 Hexagonal layered structure of TiS TiS, L AYERS 2' P age -8bF igure 2 1-T c oordination of chalcogen atoms with respect to the transition metal atom. T RIGONAL A NTIPRISM Titanium P age - 8c- F igure 3 2-N c oordination of chalcogen a toms w ith respect to the'transition metal atom. T RIGONAL P RISM T itanium P age - 9 - t he structural, optical and electrical properties of the transition metal dichalcogenides has been documented by Wilson and Yoffe (30). 2 - 2 ( a ) T itanium Disulphide S ,toichiometric T iS 2 - C rystal Structure c rystallizes in only one stable state forming a layered crystal having a golden metallic luster. It has the C dI 2 ( trigonal antiprism) structure b elonging to the space group C 3 v w ith one formula unit per unit cell. T iS2 i s commonly referred to as I T-TiS 2 m eaning a one layer stacking sequence with a trigonal primitive unit cell (Fig. 4). E ach layer is made up of a hexagonal plane of titanium atoms sandwiched between two hexagonal planes of sulfur atoms. Chianelli et. a l . ( 42) determined the atomic positions of the titanium and sulfur atoms within the unit cell to b e: T i: O,O,O S: 1/3, 2/3, u w here u S 1 / 4 . T hompson e t . al. ( 57) f ound the lattice parameters of stoichiometric T i S 2 a t room temperature to be: Page -9a- Figure 4 TiS TiS, 2 atomic structure. S tructure 0 Sulfur Titanium c:,, P age - 10- T he T iS2 s andwich layers are bound together by a weak Van der Waals type bonding, while the titanium and sulfur atoms making...
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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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