| 1. |
- Aksenova, N.A., et al.
(author)
-
Structural studies of C60 polymerized at high pressure
- 1997
-
In: Proceedings of the Symposium on Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials. - Pennington, NJ : Electrochemical Society, Incorporated. - 1566771927
-
Conference paper (peer-reviewed)
|
|
| 2. |
- Aksenova, N.A., et al.
(author)
-
Structure studies of C60 polymerized at low pressures
- 1997
-
In: Fullerenes. - Pennington, NJ : The Electrochemical Society. - 1566771927 ; , s. 687-694
-
Conference paper (peer-reviewed)abstract
- The structure and lattice properties of a polymerized C60 sample were investigated by X-ray powder diffraction over the range from liquid-nitrogen to room temperature. The aim of these studies was to establish the effect of low-pressure compression (up to 1.1 GPa) on the phase composition of the sample, to determine the structure of the phases involved, to obtain the variation of the lattice parameters with temperature, to observe eventual phase transformation in polymerized C60, and to elucidate the evolution of the orientational order with varying temperature. Analysis of the room-temperature diffraction patterns indicates that the sample contained at least two major phases, namely rhombohedral and and tetragonal with the polymerization array close to two-dimensional. Our data obtained on samples annealed at 300 C in the air allow us to conclude that polymerized C60 converts to a mixture of the fcc structure plus a new phase, presumably C60O.
|
|
| 3. |
- Aleksandrovskii, A. N., et al.
(author)
-
Negative thermal expansion of fullerite C60 at helium temperatures
- 1997
-
In: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 23:11, s. 943-946
-
Journal article (peer-reviewed)abstract
- The thermal expansion of fullerite C60 has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below ~ 3.4 K the linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed
|
|
| 4. |
- Aleksandrovskii, A. N., et al.
(author)
-
Thermal expansion of single-crystal fullerite C60 at helium temperatures
- 2000
-
In: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 26:1, s. 75-80
-
Journal article (peer-reviewed)abstract
- The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2–10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed.
|
|
| 5. |
- Andersson, Ove, et al.
(author)
-
Reorientational relaxation in C60 following a pressure induced change in the pentagon/hexagon equilibrium ratio
- 1995
-
In: Physics Letters A. - : Elsevier Science B.V.. - 0375-9601 .- 1873-2429. ; 206:3-4, s. 260-264
-
Journal article (peer-reviewed)abstract
- The orientational structure of C60 depends on pressure and temperature. Pressurization below the glass transition temperature Tg can freeze in non-equilibrium orientational structures. The relaxation of such structures on heating through Tg has been studied through thermal conductivity measurements and the effects observed are explained in a simple model.
|
|
| 6. |
- Andersson, Ove, et al.
(author)
-
Thermal conductivity of C60 at pressures up to 1 GPa and temperatures in the range 50-300 K
- 1996
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 3093-3100
-
Journal article (peer-reviewed)abstract
- The thermal conductivity λ of C60 shows anomalies near 260 K and 90 K which are associated with the well-established phase transition and glass transition, respectively. Both transition temperatures increase with pressure, at the rates 120 K GPa-1 and 62 K GPa-1, respectively. With increasing temperature, λ of the simple cubic (sc) phase increased below 170 K (glasslike behavior) but decreased above. The glasslike behavior of λ is probably due to a substantial amount of lattice defects. Possible reasons for the change of sign of dλ/dT near 170 K are discussed. In the face centered cubic (fcc) phase (T≳260 K at atmospheric pressure) λ was almost independent of temperature, a behavior which is far from that of an ordered crystal (λ∝T-1 for T≳Debye temperature). This result can be attributed to the molecular orientational disorder of the fcc phase. The relaxation behavior associated with the glassy state and its unusually strong dependence on thermal history are discussed briefly, and data which support a previously reported relaxation model are presented. At room temperature, the density dependencies of λ, (∂ lnλ/∂ lnρ)T, were 5.5 and 9.5 for the fcc and sc phases, which are values typical for an orientationally disordered phase and a normal crystal phase, respectively.
|
|
| 7. |
- Andersson, Ove, et al.
(author)
-
Thermal conductivity of C60 under high pressure
- 1995
-
In: Science and Technology of Fullerene Materials. - Pittsburgh, PA : Materials Research Society. - 155899260X ; , s. 549-554
-
Conference paper (peer-reviewed)abstract
- We have measured the thermal conductivity lambda of highly pure polycrystalline C60 in the range 50 to 300 K under pressures up to 1 GPa. The results are discussed in terms of the lattice structure and dynamics. In particular, we discuss the phase diagram as delineated by anomalies observed in lambda and cp at the f.c.c.-to-s.c. transition at 260 K and the glass transition at Tg = 90 K, and also the effect on lambda of the orientational motion in the s.c. phase. The results are found to be compatible with a p/T phase diagram recently suggested by us.
|
|
| 8. |
- Lundin, Anders, et al.
(author)
-
Compressibility and Structure of C70
- 1995
-
In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 30:8, s. 469-474
-
Journal article (peer-reviewed)abstract
- The compressibility of C70 has been investigated by means of direct piston and cylinder measurements in the temperature range 150 to 365 K and up to 1 GPa. At 296 and 343 K we find a very rapid change of volume with pressure below 0.15 GPa. We tentatively interpret this as a continuous molecular reorientation with pressure, probably resulting in a transformation from a mixture of face-centred cubic (f.c.c.) and rhombohedral (r.h.) phases to mainly pure r.h. phase. At 365 K as well as at 236 K and below we see no anomalies indicating any structural or rotational anomalies in the pressure range investigated. The zero-pressure bulk modulus decreases with increasing temperature, from 13.1 GPa at 185 K to 7.9 GPa at 365 K. Our volumetric measurements confirm a recently proposed phase diagram for C70.
|
|
| 9. |
- Lundin, Anders, et al.
(author)
-
Compressibility of C61D2 up to 1 GPa in the temperature range 175 - 345 K
- 1996
-
In: Carbon. - : Elsevier Science Ltd.. - 0008-6223 .- 1873-3891. ; 34:9, s. 1119-1121
-
Journal article (peer-reviewed)abstract
- We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175–343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, possibly indicating pressure-induced changes in the structure. The (extrapolated) zero-p bulk modulus K(0) decreases with increasing T from 6.7 GPa at 175 K to 5.2 GPa at 343 K. A comparison with hypothetical expanded f.c.c. C60 with the same lattice constant shows that K(0) values are similar, indicating that the main intermolecular interactions are still between molecular bellies, not the sidegroups.
|
|
| 10. |
- Lundin, A., et al.
(author)
-
Compression properties and p-T phase diagrams of C60, C70, and C61D2
- 1996
-
In: Proceedings of the Symposium on Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials. - Pennington, NJ : Electrochemical Society, Incorporated. - 1566771625 ; , s. 1138-1142
-
Conference paper (peer-reviewed)
|
|
