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X 2 p age 5 t he first observation of an order

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Unformatted text preview: T i S s ample. x 2 I r educed and they attributed these modes to the formation of a I They found that new R aman m odes appeared in the spectra as the temperature was Ag-superlattice within the T iS 2 l attice. In addition they o bserved the Ag-superlattice directly in electron diffraction patterns. Leonelli et. a l . ( 22) and Plischke e t . al. ( 25) i nvestigated the temperature and silver concentration dependence of the order-disorder transition in Ag T iS x R aman s cattering experiments. 2 u sing They observed a continuous, apparently second o r d e r , transition and obtained excellent agreement with the predictions of a two-dimensional lattice b g as model. * go. 33 be T C The order-disorder transition temperature for T iS2 w as estimated from R aman s cattering experiments to = 3 0 0 K . T he continuous variation of the square of the order parameter indicated that the transition was second order but definitive conclusions about the transition could not be made because data could not be obtained close to the critical temperature T C' I n a n effort t o c onfirm the two-dimensional and second order nature of the transition Suter et. al. (23) carried out X-ray diffraction experiments on a thermally grown sample of A g0.33TiS2. T hey found that the transition appeared to be P age - 6 - s econd order due to the continuous variation of the Bragg peak intensities and did not find any "cross-over" to three dimensional behaviour. T-hey a lso found a s omewhat lower transition temperature (265 K ) t han was obtained (300 K ) f or the electro-intercalated compounds studied in the R aman s cattering experiments. Gerards e t . a l . (65) also came to the conclusion that the order-disorder transition was second order in nature and occurs at T C = 3 01 K b ased on a s eries of X -ray and electrochemical measurements on a Ag 0.33 T iS2 s ample grown by vapour transport. This work represents a n effort to obtain more definitive and complementary information on the nature of the o rdera nd in this thesis the d isorder transition in A g T iS x 2' results of differential scanning calo...
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