| 1. |
- Aleksandrovskii, A. N., et al.
(författare)
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Low-temperature thermal expansion of pure and inert gas-doped fullerite C60
- 2003
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Ingår i: Fizika Nizkikh Temperatur (Kharkov). - : AIP Publishing. - 0132-6414 .- 1816-0328. ; 29:4, s. 432-442
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Tidskriftsartikel (refereegranskat)abstract
- The low temperature (2–24 K) thermal expansion of pure (single-crystal and polycrystalline) C60 and polycrystalline C60 intercalated with He, Ne, Ar, and Kr has been investigated using the high-resolution capacitance dilatometer. The investigation of the time dependence of the sample length variations deltaL(t) on heating by deltaT shows that the thermal expansion is determined by the sum of positive and negative contributions, which have different relaxation times. The negative thermal expansion usually prevails at helium temperatures. The positive expansion is connected with the phonon thermalization of the system. The negative expansion is caused by reorientation of the C60 molecules. It is assumed that the reorientation is of a quantum character. The inert gas impurities affect the reorientation of the C60 molecules very strongly, especially at liquid helium temperatures. A temperature hysteresis of the thermal expansion coefficient of Kr– and He–C60 solutions has been revealed. The hysteresis is attributed to orientational polyamorphous transformation in these systems.
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| 2. |
- Aleksandrovskii, A.N., et al.
(författare)
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On the polyamorphism of fullerite-based orientational glasses.
- 2005
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 31:5, s. 429-444
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Edwards, Lyndon, et al.
(författare)
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Worldwide activities
- 2017
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Ingår i: Molten Salt Reactors and Thorium Energy. ; , s. 635-774
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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