| 1. |
- Aleksandrovskii, A.N., et al.
(författare)
-
On the polyamorphism of fullerite-based orientational glasses.
- 2005
-
Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 31:5, s. 429-444
-
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.
|
|
| 2. |
- Dolbin, Alexander V., et al.
(författare)
-
Specific features of thermal expansion and polyamorphism in CH4 – C60 solutions at low temperatures
- 2007
-
Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 33:12, s. 1068-1072
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the linear thermal expansion coefficient alpha(T) is investigated in the temperature range of 2.5 to 23 K for two different CH4-C-60 solutions in which CH4 molecules occupy 24 and 50% of the octahedral interstitial sites of the C-60 lattice. In both cases, alpha(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 is estimated, and the behavior of these two glasses is compared. The characteristic times of thermalization tau(1), reorientation of the C-60 molecules tau(2), and of the phase transformation between the glasses tau('), are estimated for these solutions. Both the temperature dependence of alpha(T) and the characteristic thermalization time tau(1) are found to have features near the phase transition temperature, and an explanation is put forward to explain these observed features.
|
|
| 3. |
- Dolbin, Alexander V., et al.
(författare)
-
The effect of the noncentral impurity-matrix interaction upon the thermal expansion and polyamorphism of solid CO-C60 solutions at low temperatures
- 2008
-
Ingår i: Fizika Nizkikh Temperatur. - : AIP Publishing. - 0132-6414. ; 34:6, s. 592-598
-
Tidskriftsartikel (refereegranskat)abstract
- Orientational glasses with CO molecules occupying 26 and 90% of the octahedral interstitial sites in the C60 lattice have been investigated by the dilatometric method in a temperature interval of 2.5–22 K. At temperatures 4–6 K the glasses undergo a first-order phase transition which is evident from the hysteresis of the thermal expansion and the maxima in the temperature dependences of the linear thermal expansion coefficients a(T), and the thermalization times t1(T) of the samples. The effect of the noncentral CO–C60 interaction upon the thermal expansion and the phase transition in these glasses was clarified by comparing the behavior of the properties of the CO–C60 and N2–C60 solutions.
|
|
| 4. |
- Dolbin, Alexander V., et al.
(författare)
-
Thermal expansion of solutions of deuteromethane in fullerite C60 at low temperature : Isotopic effect
- 2009
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics. - 1063-777X .- 1090-6517. ; 35:3, s. 226-231
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal expansion of CD4 solutions in the orientational glass C60 with molar concentration of deuteromethane 20 and 50% has been investigated in the temperature range 2.5–23 K. The orientational glass CD4–C60 undergoes a first-order phase transition in the temperature interval 4.5–55 K. This transition is manifested as hysteresis of the linear thermal expansion coefficient alpha as well as maxima in the temperature dependences alpha(T) and tau1(T), where tau1 is the characteristic thermalization time of the experimental samples. The characteristic re-orientation times of the C60 molecules and the characteristic phase transformations occurring in the experimental solutions are determined. The results of the present study are compared with the results of a similar study of the solution CH4–C60. It is concluded that tunneling rotation of the CH4 and CD4 molecules occupying interstitial positions in the fullerite C60 lattice occurs.
|
|
| 5. |
- Manzhelii, V.G., et al.
(författare)
-
Thermal expansion and polyamorphism of N2 – C60 solutions
- 2006
-
Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 32:7, s. 695-699
-
Tidskriftsartikel (refereegranskat)abstract
- The linear coefficients alpha(T) of N-2-C-60 solutions with 9.9% and 100% of the C-60 lattice thermal expansion interstitials filled with N-2 are investigated in the interval 2.2-24 K. The dependence alpha(T) has a hysteresis suggesting co-existence of two types of orientational glasses in these solutions. The features of the glasses are compared. The characteristic times of phase transformations in the solutions and reorientation of C-60 molecules are estimated.
|
|
| 6. |
- Dolbin, Alexander V, et al.
(författare)
-
Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures.
- 2008
-
Ingår i: Fizika Nizkikh Temperatur. - : AIP Publishing. - 0132-6414. ; 34:8, s. 860-862
-
Tidskriftsartikel (refereegranskat)abstract
- For the first time, the linear coefficient of radial thermal expansion is measured on a system of carbon single-walled nanotube (SWNT) bundles at low temperatures (2.2–120 K). The measurements are performed using a dilatometer with a sensitivity of 2×10−9 cm. A cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of nanotubes are oriented perpendicular to the sample axis. The starting powder consisted of over 90% SWNTs with outer diameter 1.1 nm, the length varying in the range 5–30 µm. A change of sign of the radial thermal expansion coefficient at 5.5 K is observed.
|
|
| 7. |
- Dolbin, Alexander V., et al.
(författare)
-
Radial thermal expansion of pure and Xe-saturated bundles of single-walled carbon nanotubes at low temperatures
- 2009
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 35:6, s. 484-490
-
Tidskriftsartikel (refereegranskat)abstract
- The radial thermal expansion coefficient alphar of pure and Xe-saturated bundles of single-walled carbon nanotubes (CNTs) is measured in the interval 2.2–120 K. The coefficient is positive above T=5.5 K and negative at lower temperatures. The experiment was done using a low-temperature capacitance dilatometer with a sensitivity of 2×10−9 cm, and the sample was prepared by compacting a CNT powder in such a way that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion, while the solid compacted material has a positive expansion coefficient due to expansion of the intertube volume in the bundles. Doping the nanotubes with Xe caused a sharp increase in the magnitude of alphar in the whole range of temperatures used and gave rise to a peak in the dependence alphar(T) in the interval 50–65 K. A subsequent decrease in the Xe concentration lowered the peak considerably but had little effect on the thermal expansion coefficient of the sample outside the region of the peak. The features revealed are explained qualitatively.
|
|
| 8. |
- Dolbin, Alexander V., et al.
(författare)
-
The effect of sorbed hydrogen on low-temperature radial thermal expansion of single-walled carbon nanotube bundles
- 2009
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 35:12, s. 939-943
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of a normal H2 impurity upon the radial thermal expansion ar of single-walled carbon nanotube (SWNT) bundles has been investigated in the interval T = 2.2–27 K using the dilatometric method. It is found that H2 saturation of SWNT bundles causes a shift of the temperature interval of the negative thermal expansion towards lower (as compared to pure carbon nanotubes) temperatures and a sharp increase in the magnitude of ar in the whole range of temperatures investigated. The low temperature desorption of H2 from a powder consisting of bundles of SWNTs, open and closed at the ends, has been investigated.
|
|
| 9. |
- Dolbin, Alexander Vitoldovich, et al.
(författare)
-
Influence of dissolved oxygen on the thermal expansion and polyamorphism of fullerite C60
- 2007
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 33:5, s. 465-471
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the coefficient of linear thermal expansion alpha of O-2-C-60 solutions with 20% and 80% filling of the octahedral cavities with oxygen is investigated in the temperature interval 2.2-24 K. Hysteresis of alpha(T) is observed, attesting to the coexistence of two orientational glasses in these solutions. A comparison of the behavior of these glasses is made. The characteristic times for reorientation of the C-60 molecules and for the phase transformations in the solutions are determined. When the temperature of the O-2-C-60 solution with 20 mol.% oxygen is increased to 450 degrees C, a chemical interaction of the oxygen with the C-60 molecules is manifested. It proves possible to separate the influences of the chemical and physical sorption of oxygen on the thermal expansion of polycrystalline fullerite C-60.
|
|
