Studies on Phase Transitions by AC Calorimetry

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Abstract
As examples of the best use of the so-called AC calorimetry technique, several results are described from various viewpoints. The behavior of heat capacity at ferroelectric, antiferroelectric and structural phase transitions is surveyed from the standpoint of critical behavior, of jump at first order transition, or of a sensitive metod of finding a new phase transition. In two- and three-dimensional antiferromagnets, the critical behavior is discussed with an emphasis on the crossover from the Ising to the Heisenberg system. In the two-dimensional antiferromagnets, the crossover is revealed from the dependence of the critical amplitude on the strength of the Ising-like anisotropy. A hyperscaling relation is proposed at nematic-to-smectic A transition of liquid crystals. Finally, studies of the frequency dependence of heat capacities in the denaturation of proteins and in the order-disorder transition of alloys are reported.