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2 d ependent on the fraction of titanium residing in the Van der
Waals gap. The titanium in the Van der Waals gap increases
the interlayer interaction inhibiting the mobility of the
intercalated species and possibly preventing the
intercalation of some species ( 33, 4 7, 5 3 ) .
O ptical experiments ( 5 4 , 5 5 ) i ndicate that T i S 2 is a s emiconductor and calculations by Zunger et. al. (61) P a g e - 15i ndicate an indirect band gap of 0 . 2 - 0 . 3 ev. O n the other hand temperature dependent resistivity measurements by
Thompson et. a l . ( 44) w ere interpretted to indicate that T iS2
e xibits s e m i - m e t a l l i c properties.
observations c a n be reconciled These conflicting (30) by assuming that T i S 2 i s a " dirty semiconductor" meaning that even in
stoichiometric T i S s ome of the titanium atoms may be 2 displaced from their usual locations and reside a t vacant
interlayer s i t e s . Moret e t . a l . ( 6 2 ) modelled the effect of intersital titanium atoms to explain various anomalies in
X-ray diffraction patterns of Ti S
l + x 2' T hompson e t . al. ( 5 7 ) have found that the lattice parameters varied with the S /Ti
ratio. They have measured the variation in the lattice parameters and the density as a f u n c t i o n of the S /Ti r atio
(for S /Ti i n the range 1 . 8 0 - 2 .00) and plotted the results ( 63), t hus providing a direct method for determining the
stoichiometry of T i S 2 s amples from the lattice parameters. 2 - 3 ( a ) Intercalation of T iSZ P owders
T h e insertion of guest atoms or molecules between the
layers of a host ( l a y e r e d compound), without altering the
atomic structure of the host l a t t i c e , is generally referred
to a s intercalation if the process is r e v e r s i b l e . T h e guest species that has been successfully intercalated resides
within the Van der Waals gap between the layers of the
t ransition m etal dichalcogenide c o m p o u n d s . . Recent work (33) P age - 1 6 h as shown that Group I b , l a , I I b , I Ia e lements, aluminum,
gallium, indium, thallium, a s well as ammonia (or substituted
ammonium compounds) can be intercalated into the transition
metal dichalcogenides. The m...
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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.
- Fall '09