  The dilatometric investigation in the temperature range of 2-28K 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 12K. 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 non-interacting 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.
