On the polyamorphism of fullerite-based orientational glasses.

• The dilatometric investigation in the temperature range of 2–28 K shows that a first-orderpolyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 andXe. A polyamorphous transition was also detected in C60 doped with Kr and He. It is observed thatthe hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transitiontemperature) is essentially dependent on the type of doping gas. Both positive and negativecontributions 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 positivecontribution. The positive contribution is found to be due to phonon and libron modes, whilst thenegative contribution is attributed to tunneling states of the C60 molecules. The characteristictime of the phase transformation from the low-T phase to the high-T phase has been found for theC60–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 inglasses, as well as the thermodynamics and kinetics of the transition. A model of noninteractingtunneling states is used to explain the negative contribution to the thermal expansion. The experimentaldata obtained is considered within the framework of the theoretical model. From the theoreticalmodel 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 theKolmogorov law with an exponent of n = 1. At this stage of the transformation, the two-dimensionalphase boundary moves along the normal, and the nucleation is not important.

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Fullerenes

C60

thermal expansion

polyamorphism

orientational glass

hydrogen

Xenon

deuterium

H2

Xe

D2

intercalation

transition temperature

krypton

helium

phonons

tunneling

Condensed matter physics

Kondenserade materiens fysik

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