Heat capacity measurements were performed for Se, Se90Te10, Se80Te20, and Se70Te30 materials in the 230-630 K temperature range. Both glassy and crystalline Cp dependences were found to be identical within the experimental error. The compositional dependence of the N-type undercooled liquid Cp evolution was explained on the basis of free-volume theory; vibrational and chemical contributions to heat capacity were found to be roughly similar for all Se-Te compositions. The thermal behavior in the Se-Te chalcogenide system was thoroughly studied: glass transition, cold crystallization, and melting were investigated in dependence on composition and various experimental conditions (heating rate, particle size, and pre-nucleation period). The kinetics of the structural relaxation and crystallization processes are described in terms of the Tool-Narayanaswamy-Moynihan and Johnson-Mehl-Avrami models. The complexity of these processes is thoroughly discussed with regard to the compositionally determined changes of molecular structures. The discussion is conducted in terms of the mutual interplay between the thermodynamics and kinetics in this system.

Faculty of Chemical Technology Department of Physical Chemistry University of Pardubice Studentska 573 532 10 Pardubice Czech Republic

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Kinetic Processes in Amorphous Materials Revealed by Thermal Analysis: Application to Glassy Selenium