Calorimetric measurements of the phase transition in Rochelle salt–ammonium Rochelle salt mixed crystals

概要

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The specific heats, which are given with absolute value, of Rochelle salt–ammonium Rochelle salt mixed crystals (RS1-x−ARSx) in a region 0.18<~x<~0.9 have been measured between about 10 K and 300 K by an ac calorimetric method. A very small anomaly was found around the transition for any x. It becomes larger as x increases. The anomalies have been well described using the Landau-type free energy expanded to the sixth order of polarization. It was found that, as x increases, the transition point approaches the tricritical point at which a crossover from the second-order phase transition to the first-order one takes place. Transition entropy has been calculated from the anomalous specific heat. It increases from about 8% to about 55% of Rln2 with increasing x in the measured region. Very small values for small x in this region suggest the displacivelike character in the phase transition. And the order-disorder motion contributes more and more to the phase transition with increasing x.
American Physical Societyの論文
2000-11-01