Abstract:
Measurements of the heat capacity of Fe9S a0 over the temperature range 5 K to 740 K reveal a first-order structural transition at 495 K and t~vo higher-order transitions with maxima at 534 K and 591 K. The last two are of coupled magnetic and structural origin. The structural changes giving rise to the heat-capacity effects are identified, and the magnetic properties are interpreted in terms of these. The standard entropy at 298.15 K of (1/19)F%S10 is compared with those of (1/2)FeS and (1/15)FeTSs. The origin of the higher molar entropy for the first compound is found to reside mainly in the higher electronic heat-capacity contribution. The thermodynamic properties for (1/10)FeaS10 have been evaluated and the values of Cp, m, Ao~Sm, and A~H m are 6.171. R, 7.598. R and 1147.3. R. K at 298.15 K and are 6.944. R, 14.524-R, and 4572.4. R. K at 740 K. (R = 8.31441 J. K- 1. mol- 1).
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