Fizika Nizkikh Temperatur: Volume 44, Number 8 (August 2018), p. 1062-1072 ( to contents , go back )
IR studies of thermally stimulated structural phase transformations in cryovacuum condensates of Freon 134a
A. Drobyshev, A. Aldiyarov, A. Nurmukan, D. Sokolov, and A. Shinbayeva
Al-Farabi Kazakh National University, Almaty 050038, Kazakhstan
Received February 18, 2018
The method of cryovacuum condensation of thin gas films with the formation, including the glassy states provides ample opportunities for precise control and maintenance of the formation conditions of studied samples. It allows researchers to formulate and solve the question of the relationship between the formation conditions and the structure of molecules on the one hand, and the degree of kinetic stability of cryocondensates, including organic glasses. In this study, the objects of investigation are thin films of Freon 134a cryovacuum condensates condensed on a cooled metal substrate from the gas in the deposition temperatures range from 16 to 100 K and the gas phase pressures from 10–4 to 10–6 Torr. A comparison between the vibrational spectra of Freon 134a in the gas phase and in the cryocondensed state is given. The results of IR spectrometric studies of cryovacuum condensates of Freon 134a 2.5 μm thick in the frequency range 400–4200 cm–1 are presented. On the basis of the obtained spectra and data on their thermally stimulated transformations, it is assumed that in the temperature range 16–60 K Freon 134a cryocondensates are in an amorphous state with different degrees of amorphization. At the temperature Tg = 70 K, a transition from the amorphous glassy state to the state of the super-cooled liquid phase takes place, followed by its crystallization into the state of a plastic crystal. In the temperature range 78–80 K, the transition of a plastic crystal to a crystalline state with a monoclinic lattice begins.
PACS: 61.50.–f Structure of bulk crystals;
Key words: Freon, crystallization, structural transformations, cryovacuum condensates, vitrification.
Published online:: June 27, 2018