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Pure Appl. Chem., 2005, Vol. 77, No. 8, pp. 1331-1343

Entropy diagnosis for phase transitions occurring in functional materials

Michio Sorai

Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

Abstract: Functionalities of materials manifest themselves as the result of a concerted effect among molecular structure, intermolecular interactions, and molecular motions. Since the entropy of substance directly reflects the degree of molecular motions, the entropy plays a crucial role when one discusses the stability of a given phase at finite temperatures. When a delicate balance of these three factors is broken, the condensed state faces a catastrophe and is transformed into another phase. Therefore, phase transition is a good probe for elucidation of the interplay between these three factors. As there is no selection rule in thermodynamics, the entropy gain at the phase transition is a good tool to diagnose the mechanism of phase transition. In this presentation, calorimetric investigations aimed at the elucidation of the mechanisms governing phase transitions occurring in molecule-based functional materials are reviewed.