P age 52a f igure 22 dhdt v ersus temperature for

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Unformatted text preview: Patterns - G r o u p B ( quenched 1 0 0 0 C ) L ow temperature X-ray diffraction data were obtained from the x s amples. = 0 . 1 5 and x = 0 . 2 0 group R ( quenched from 1000 C ) Extra diffraction lines were found in the X-ray patterns for A g T i S 2 a nd A g o , Z 0 T i S 2 w h e n the samples w e r e 0.15 cooled to 150 K . T h e extra lines were attributed to the formation of a superlattice of A g atoms within the host T i S 2 P a g e - 54- l attice. T h e extra lines were identified as belonging to a J3.ao x J3a 0 x c 0 s uperlattice (where a 0 and c 0 are the l attice parameters of the host T i S o ccupancy of A g a toms forming a (a 3 2 s tructure). 0 x J3a0 T he i deal s uperlattice i s 1/6 f or a stage 2 c ompound and 1 / 3 f or a stage 1 c ompound although S choltz ( 63) r eports that the Ag concentration in stage 2 m ay overfill to x x = 0.20 a nd overfill in stage 1 t o = 0.42. 5 -5 ( a) Specific Heat Measurement T h e specific heat of the batch B s amples (quenched from 1000 C ) w ith silver mole fraction i n the range 0 < x < 0 . 5 w as determined. Sample sizes of 1 5 t o 3 5 m g . were hermetically sealed in aluminum sample pans and were run against identical empty sample pans in order to cancel the effects due to the spectific heat o f t he sample pans. - f or measurements far away from the transition r e g i o n s , equation 4-1 r educes to d /dt(T - T ) Sr = 0 a nd d h/dt =0 b ecause the sample undergoes no transitions and therefore P age - 5 5 - I n t his equation C i s the specific heat of the sample S m aterial plus the specific heat of the sample pan or 'S -m ' + C r a nd thus Equation 5 -1 s hows that the measured quantity - (TS-Tr)/R is equal to the specific heat of the sample material ( C ) m m ultiplied by the programmed h eating/cooling r ate ( dT / dt) P w hen the reference material is an empty pan identical to the pan containing the sample material and when the sample does not undergo a transition. 5 - 5 ( b ) S pecific Heat Procedure and Results Three consecutive heating-cooling scans were taken for each sample to eliminate spurious results and reduce the effects of time dependent character...
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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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