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Their calculated values were in excellent agreement 5

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Unformatted text preview: reference 5 2 ) . F ig. 0.35 9 of Page - 5 9 - C HAPTER 6 CONCLUSIONS H igh quality T i S 2 p owders were successfully prepared from the elements. T h e s t o i c h i o m e t r y , structural quality and grain size of the powders were investigated and monitored using X-ray f l o u r e s c e n c e , X-ray diffraction and electron microscopy techniques. Differential scanning calorimetry runs were carried out on the A g T i S x 2 s amples for temperatures in the range 1 70 K < T < 600 K . T h e critical temperature Tc for the intercalate order-disorder transition was found to be 2 6 8 2 2 K f or x < 0 . 1 5 (stage 2) and 2 8 8 2 2 K f or all concentrations x g reater than or equal to 0 . 2 0 . T h e i ndependence of Tc of x for x > 0 . 2 0 could be explained by accumulation of e xcess A g in pockets or on the surface. This is also consistent with the invariant appearance of t heJ3 s uperlattice for all concentrations greater than or equal to 0 . 1 5 ( 2 1 , 2 2 , 31). There was no observable hysteresis in the critical temperature Tc to within the limits of the experimental accuracy ( 2 1 .0 K ). T h i s observation is also consistent w i t h previous observations. Leonelli et. a l . ( 22), S uter et. al. (23) and Plischke e t . a l . (25) all observed behaviour that led them to conclude that the order-disorder transition was second order in n a t u r e . ' T h e lack of hysteresis in Tc P a g e - 60c orroborates these previous results. T h e D SC a pparatus was used to measure the specific heat o f t he u nintercalated T i S 2 powders. A v alue o f 1 7 . 3 2 1 . 0 c al./mole-K w as obtained with the sample at 3 0 0 K. This value is in reasonable agreement with the r esult ( 1 6 . 2 3 c al/mole-K) o btained previously by Todd and Coughlin (66). U sing pristine T i S 2 a s a r e f e r e n c e , the specific heat of the A gxTiS2 p owders was also measured and was found t o i ncrease steadily with increasing temperature. specific heat near Tc (for x = T h e variation in the 0 . 4 0 ) was compared to the results predicted by Schick et...
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