Hysteretic phenomena in Xe-doped C60 from x-ray diffraction

Self Cite

The temperature dependence of the linear thermal expansion coefficient a(T) has been investigated in the temperature range of 2.5 to 23 K for two different CH 4 -C 60 solutions in which CH 4 molecules occupied 24 and 50% of the octahedral interstitial sites of the C 60 lattice. In both cases, a(T) exhibits hysteresis, suggesting the existence of two types of orientational glass associated with these solutions. The temperature of the first-order phase transition between these two glasses was estimated and the behavior of these two glasses compared. The characteristic times of thermalization t 1 , reorientation of the C 60 molecules t 2 , and of the phase transformation between the glasses t¢, have been estimated for these solutions. Both the temperature dependence of a(T) and the characteristic thermalization time t 1 are found to have features near the phase transition temperature and an explanation has been put forward to explain these observed features.PACS: 74.70.Wz Fullerenes and related materials.

Section: Introductionmentioning

confidence: 57%

Specific features of thermal expansion and polyamorphism in CH4–C60 solutions at low temperatures

Долбин

Esel'son

Gavrilko

et al. 2007

Self Cite

“…Transitions between those orientational-glass states are polyamorphic transformations, which can be of first order. However, it should be mentioned here that x-ray diffraction experiments [13] actually on the same sample revealed an incomparably larger hysteresis in the temperature dependence of the lattice parameter, spanning a range from 150 K across the phase transition point at 260 K to about The dash curves are absent in Devonshire's theory. 300 K. On the other hand, since the temperatures are low enough to exclude thermal activation, the next assumption was that the rotations, which take place between orientational glass states, should have tunnel nature, which was also substantiated by negative expansivities.…”

Section: Thermal Expansion Of Pure and Doped C 60 At Low Temperaturesmentioning

confidence: 83%

Novel carbon materials: New tunneling systems (Review Article)

Strzhemechny

Долбин

2013

Self Cite

This review covers recent achievements in the studies of quantum properties of the novel carbon materials (fullerite C 60 and bundles of single-walled nanotubes (SWNT)) saturated with such light-mass species as helium isotopes, the homonuclear molecular hydrogens, and neon. It is shown that even some heavy dopants demonstrate kinetic phenomena, in which coherent effects play an essential role. Two theoretical concepts are surveyed which have been suggested for the explanation of the anomalous phenomena in saturation kinetics and linear thermal expansion of doped C 60 . Most unusual effects have been also observed in the low-temperature radial expansion of bundles of single-walled carbon nanotubes saturated with the helium isotopes. First, it was shown that low-temperature radial expansion of pure SWNT is negative, i.e., a nanotube shrinks with warming. Second, saturation of SWNT bundles with the helium isotopes entails a huge increase of the negative expansion effect, when the dopant is He. So far, no detailed physical picture has been put forward. It is worth mentioning that the dynamics of a single helium atom on an isolated nanotube corresponds to that of a tight-bound quasiparticle with a band width of about 10 K.

“…The other weak reflections observed are marked with arrows in Fig. 1, and these may correspond to diffraction by an additional phase formed (like in [6]) by partial polymerization of the C 60 as a result of the high-pressure compaction. This assumption is supported by the fact that the x-ray diffraction patterns taken of the powder resulting from gently crushing a compacted samples showed only the reflections from fcc C 60 -N 2 alloys, with these weak reflections now absent.…”

Section: Resultsmentioning

confidence: 99%

Intercalation of fullerite C60 with N2 molecules. An investigation by x-ray powder diffraction

Galtsov

Prokhvatilov

Dolgova

et al. 2007

Self Cite

The lattice parameter a of fullerite C 60 intercalated with N 2 molecules is investigated in the temperature interval 6-295 K by x-ray diffraction. It is found that the interstitial molecular N 2 has a considerable effect on both the temperatures, T c of the orientational phase transition and T g of the orientational glass formation. Hysteresis of a(T) has been detected in the T c and T g regions, besides, the abrupt change in the volume over the region defining T c . Complete intercalation of C 60 with N 2 molecules results in a 0.2% increase in the lattice parameter, which persists over the whole temperature range. Evidence is also obtained that the interstitial guest molecular N 2 induces a slight deformation of the cubic symmetry of the host C 60 lattice. PACS