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Kokshenev V. B. Loosing thermodynamic stability in amorphous materials [Електронний ресурс] / V. B. Kokshenev // Физика низких температур. - 2011. - Т. 37, № 5. - С. 551-557. - Режим доступу: http://nbuv.gov.ua/UJRN/PhNT_2011_37_5_21 The primary relaxation dynamics near the glass transformation temperature Tg exhibits universal features in all glass formers, when showing two-level tunneling states (Low Temp. Phys. 35, 282 (2009)). Researchers have long searched for any signature of the underlying "true" ergodic-nonergodic transition emerging at a certain thermodynamic instability temperature Te. Here, the relaxation timescale for glass-forming materials is analyzed within a self-consistent thermodynamic cluster description combined with the cluster percolation concept. Exploring the ergodic hypothesis, its violation is found near a crossover from the Gaussian to non-Gaussian (Poisson) cluster-volume fluctuations, describing the finite-size fractal-cluster distributions. The transformation of the compact-structure "ergodic" clusters into hole-like glassy nanoclusters is attributed to the critical-size thermal fluctuations. The ergodic - nonergodic phase diagram showing Te is predicted in the model-independent form through the glass fragility parameter known for organic and inorganic liquids and amorphous solids. In all cases the ergodic-instability temperature is located below and close to the glass transformation temperature, whereas the distance between the two characteristic temperatures decreases with growing the material fragility.
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Kokshenev V. B. Generic features of the primary relaxation in glass-forming materials [Електронний ресурс] / V. B. Kokshenev // Физика низких температур. - 2017. - Т. 43, № 8. - С. 1174-1188. - Режим доступу: http://nbuv.gov.ua/UJRN/PhNT_2017_43_8_13 We discuss structural relaxation in molecular and polymeric supercooled liquids, metallic alloys and orientational glass crystals. The study stresses especially the relationships between observables raised from underlying constraints imposed on degrees of freedom of vitrification systems. A self-consistent parametrization of the <$E alpha>-timescale on macroscopic level results in the material-and-model independent universal equation, relating three fundamental temperatures, characteristic of the primary relaxation, that is numerically proven in all studied glass formers. During the primary relaxation, the corresponding small and large mesoscopic clusters modify their size and structure in a self-similar way, regardless of underlying microscopic realizations. We show that cluster-shape similarity, instead of cluster-size fictive divergence, gives rise to universal features observed in primary relaxation. In all glass formers with structural disorder, including orientational-glass materials (with the exception of plastic crystals), structural relaxation is shown to be driven by local random fields. Within the dynamic stochastic approach, the universal subdiffusive dynamics corresponds to random walks on small and large fractals.
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