On the polyamorphism of fullerite-based orientational glasses

• Published in: Физика низких температур
• Date: 2005
• Main Authors: Aleksandrovskii, A.N., Bakai, A.S., Cassidy, D., Dolbin, A.V., Esel’son, V.B., Gadd, G.E., Gavrilko, V.G., Manzhelii, V.G., Moricca, S., Sundqvist, B.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2005
• Subjects: Динамика кристаллической решетки
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/121464
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: On the polyamorphism of fullerite-based orientational
 glasses / A.N. Aleksandrovskii, A.S. Bakai, D. Cassidy, A.V. Dolbin, V.B. Esel’son,
 G.E. Gadd, V.G. Gavrilko, V.G. Manzhelii, S. Moricca, and B. Sundqvist // Физика низких температур. — 2005. — Т. 31, № 5. — С. 565-584. — Бібліогр.: 38 назв. — англ.

The dilatometric investigation in the temperature range of 2–28 K shows that a first-order
 polyamorphous transition occurs in the orientational glasses based on C₆₀ doped with H₂, D₂ and
 Xe. A polyamorphous transition was also detected in C₆₀ doped with Kr and He. It is observed that
 the hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transition
 temperature) is essentially dependent on the type of doping gas. Both positive and negative
 contributions to the thermal expansion were observed in the low-temperature phase of the glasses.
 The relaxation time of the negative contribution occurs to be much longer than that of the positive
 contribution. The positive contribution is found to be due to phonon and libron modes, whilst the
 negative contribution is attributed to tunneling states of the C₆₀ molecules. The characteristic
 time of the phase transformation from the low-T phase to the high-T phase has been found for the
 C₆₀–H₂ system at 12 K. A theoretical model is proposed to interpret these observed phenomena.
 The theoretical model proposed, includes a consideration of the nature of polyamorphism in
 glasses, as well as the thermodynamics and kinetics of the transition. A model of noninteracting
 tunneling states is used to explain the negative contribution to the thermal expansion. The experimental
 data obtained is considered within the framework of the theoretical model. From the theoretical
 model the order of magnitude of the polyamorphous transition temperature has been estimated.
 It is found that the late stage of the polyamorphous transformation is described well by the
 Kolmogorov law with an exponent of n = 1. At this stage of the transformation, the two-dimensional
 phase boundary moves along the normal, and the nucleation is not important.