Structural and elastic anisotropy of carbon phases prepared from fullerite C60

Article abstract of DOI:10.1063/1.1625432

The structural and elastic anisotropy of carbon phases obtained in nonhydrostatic conditions by heating fullerite C₆₀ were studied. Two-dimensional rhombohedral polymers of C₆₀ and disordered graphite-type phases were considered. A direct correlation between textured polymerized and/or textured covalent structure and anisotropic elasticity was observed. The results show that this anisotropy is induced by the uniaxial pressure component and is governed by the uniform pressure magnitude in disordered atomic-based phases.

Full text of DOI:10.1063/1.1625432

Structural and elastic anisotropy of carbon phases prepared from fullerite C 60
A. G. Lyapin, V. V. Mukhamadiarov, V. V. Brazhkin, S. V. Popova, M. V. Kondrin, R. A. Sadykov, E. V. Tat’yanin,
S. C. Bayliss, and A. V. Sapelkin
Citation: Applied Physics Letters 83, 3903 (2003); doi: 10.1063/1.1625432
View online: http://dx.doi.org/10.1063/1.1625432
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APPLIED PHYSICS LETTERS
VOLUME 83, NUMBER 19
10 NOVEMBER 2003
Structural and elastic anisotropy of carbon phases prepared
from fullerite C60
A. G. Lyapin, V. V. Mukhamadiarov, V. V. Brazhkin, S. V. Popova, M. V. Kondrin,
R. A. Sadykov, and E. V. Tat’yanin
Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow region, 142190, Russia
S. C. Bayliss and A. V. Sapelkin
Department of Chemistry, School of Applied Sciences, De Montfort University, The Gateway, Leicester,
LE1 9BH, United Kingdom
͑
Received 25 April 2003; accepted 23 September 2003͒
We show that application of nonhydrostatic pressure to cluster-based molecular material, like
fullerite C , provides an opportunity to create elastically and structurally anisotropic carbon
6
0
materials, including two-dimensional polymerized rhombohedral C and superhard graphite-type
6
0
2
(
sp ) disordered atomic-based phases. There is direct correlation between textured polymerized
and/or textured covalent structure and anisotropic elasticity. Whereas this anisotropy is induced by
the uniaxial pressure component, in the case of disordered atomic-based phases, it may be governed
by the uniform pressure magnitude. © 2003 American Institute of Physics.
͓
DOI: 10.1063/1.1625432͔
The synthesis of carbon phases attracts considerable at-
tention in materials science, since many carbon materials
combine a low density with superior mechanical characteris-
tics ͑such as hardness and strength͒ and stability against ther-
anisotropy of structural and elastic properties that correlate
across samples, and that this anisotropy can be an experi-
mentally controlled parameter. The primary anisotropy of
synthesis pressure, that is, the uniaxial component, occurs
naturally in the quasihydrostatic conditions that occur in
toroid-type chambers21 with a single loading axis. Two-
dimensional rhombohedral polymers of C60 and disordered
1
mal degradation. The discovery of fullerenes and, in particu-
lar, the preparation of solid crystalline fullerite C60 in
2
macroscopic amounts have stimulated new efforts and pro-
2
vided new routes for synthesis of carbon-based materials.
Pressure–temperature treatment of molecular carbon crystals
of C60 provides the possibility of synthesizing engineered
materials with a variable nanostructure, nanomorphology,
graphite-type (sp ) phases are among the materials under
consideration.
The samples were synthesized from fullerite powder
with C60 content not less than 99.9%. The C60 powder was
pressed into cylinders with the 3 mm height and 4 mm di-
ameter. Toroid-type chambers21 were used for high-
pressure–high-temperature ͑0–8 GPa and 600–1400 °C)
2
3
type of bonding (sp /sp ratio͒, dimension of covalent con-
nectivity ͓one ͑1D͒-, two ͑2D͒-, or 3-dimensional ͑3D͔͒, de-
gree of polymerization ͑for molecular-type structures͒, and
3
–5
3
so on.
Among pressure-synthesized C -based phases, several
generation in a large volume ͑up to 50 mm ). The samples
were synthesized in Pt or Cu cells with the outer graphite
container serving simultaneously as a heater. The tempera-
ture was measured by chromel–alumel thermocouples. The
structure of samples was examined by conventional x-ray
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0
ordered and disordered modifications have been clearly iden-
tified to date, including crystalline 1D and 2D C
6
0
6
–9
2
polymers, very hard graphite-type (sp -based͒ disordered
7
,10,11
phases,
polymerization,
3D polymers with a varying degree of
diffraction ͑XRD, Cu K ). The synthesized materials were
␣
1
2–15
3
diamond-like (sp -based͒ amorphous
obtained in the shape of cylinders, which were used to pre-
pare samples in the shape of parallelepipeds with character-
istic dimensions 1.5ϫ1.5ϫ1.2 mm. Ultrasonic velocities
were obtained from the determination of the time of flight of
10 MHz shear or compression ultrasonic pulses (ϳ1 ␮s).
The pulse flight times in the sound line with or without a
sample were determined to an accuracy of a few nanosec-
onds.
1
4–16
14,15,17
phases,
Many of these phases are superhard materials
are potentially interesting for practical applications.
and diamond–graphite nanocomposites.
4
,5,10–15,17
and
5
,15
The recent observations of structural1 and ultrasonic20
directional anisotropy in samples synthesized from C60 under
nonhydrostatic conditions, make possible a systematic study
of the relationships between the high-pressure synthesis con-
ditions, anisotropic structure, and corresponding nonuniform
elasticity. This latter is of interest since the anisotropy of
carbon materials may be an interesting property for certain
applications; for example, as a method of increasing me-
chanical characteristics in particular directions.
8,19
In the first series of experiments, we synthesized
samples of the 2D polymerized C60 rhombohedral phase in
nonhydrostatic conditions at pressures from 3.5 to 7 GPa.
The temperature interval chosen for the synthesis ͑from 600
to 800 °C) allowed us to avoid the effects of partial
polymerization.4 In addition, the chosen pressure interval
and scheme of synthesis, that is, pressurizing and subsequent
heating, prevented the formation of dominant amounts of
,7
Here, we report the systematic study of carbon phases
obtained in nonhydrostatic conditions by heating fullerite C60
in the pressure range up to 8 GPa. In particular, we show that
the samples produced in such a way display orientational
8
tetragonal 2D polymerized C . Figure 1͑a͒ shows the lon-
6
0
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003-6951/2003/83(19)/3903/3/$20.00 3903 © 2003 American Institute of Physics
30.113.126.253 On: Wed, 26 Nov 2014 14:58:30
0
1

3904
Appl. Phys. Lett., Vol. 83, No. 19, 10 November 2003
Lyapin et al.
2
FIG. 2. Anisotropy of the superhard graphite-type (sp ) atomic-based
phases revealed by ͑a͒ longitudinal ultrasonic velocities plotted as a function
of the synthesis pressure, ͑b͒ XRD patterns ͑with the subtracted middle
lines͒ recorded in reflection mode for different geometries of the scattering
vector. There is a direct correlation between the ratios of longitudinal ve-
locities and the fractions of differently oriented graphite-like clusters ͑c͒.
FIG. 1. Anisotropy of the 2D polymerized rhombohedral C60 phases re-
vealed by ͑a͒ longitudinal ultrasonic velocities plotted as a function of the
synthesis pressure, ͑b͒ XRD patterns ͑with the subtracted middle lines͒ re-
corded in reflection mode for different geometries of the scattering vector,
and ͑c͒ 3D plot of intensity from the 2D diffraction image obtained in
transmission mode with the x-ray beam along the X axis.
gitudinal velocities of these samples, and typical diffraction
patterns from these samples are presented in Fig. 1͑b͒.
The ultrasound velocities along the Z axis ͓Fig. 1͑a͔͒,
corresponding to the direction of load in high-pressure cham-
bers, are systematically higher by Ϸ30% than those along
the X axis for all experimental pressures ͑here, the X axis is
perpendicular to Z and to the side facets chosen for the ul-
trasonic measurements͒. This observation is evidently related
to a higher degree of polymerization along the loading axis,
and this is directly confirmed by XRD ͓Fig. 1͑b͔͒. All the
reflections observed for the different geometries of recording
diffraction can be attributed to the rhombohedral 2D poly-
mers of C , whereas the behavior of peak intensities indi-
cates a strongly textured structure of the material. In particu-
lar, the peaks identified as ͑110͒, ͑120͒, and ͑220͒ are the
most intense in the diffraction patterns recorded with the
x-ray scattering vector oriented along the Z axis, while the
reflections ͑003͒, ͑014͒, and ͑006͒/͑015͒ are intense in the
diffraction patterns recorded for the perpendicular geometry.
Here, the plane ͑003͒ is parallel to the plane of polymeriza-
tion of C60 molecules in the 2D polymer. This directly sup-
ports the conclusion about a higher degree of polymerization
diffraction intensity in Fig. 1͑c͒ shows a more detailed pic-
ture of XRD from the anisotropic textured rhombohedral
polymer, displaying both broad features and sharp maxima.
The second series of synthesized samples consisted of
the disordered graphite-type (sp ) phases of hard carbon
and was obtained upon heating to temperatures from 1000 to
2
10,11
1200 °C. A quite unexpected result ͓Fig. 2͑a͔͒ for the disor-
2
dered sp phases was that the ultrasonic velocities along the
X axis proved to be higher than the corresponding velocities
along the Z axis ͑for preparation pressures higher than 4
GPa͒; that is, the inverse relation with respect to those ob-
served for the preceding 2D polymers of C . We assume
6
0
that the differences in the sound velocity propagations along
and across the Z axis are associated with a predominant ori-
entation of graphite-like clusters in the nanometer-scale tex-
tured material. Indeed, the elastic anisotropy is directly con-
firmed by the difference in the corresponding XRD patterns
͓Fig. 2͑b͔͒. XRD clearly shows the predominant orientation
of graphite-like clusters with graphene-like sheets perpen-
dicular to the Z axis.
6
0
The observed elastic anisotropy changes significantly
with the uniform component of pressure, displaying an in-
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along the axis of loading; that is, along Z. The 3D image of
version of anisotropy at Ϸ4 GPa ͓Fig. 2͑a͔͒, and can be
1
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Appl. Phys. Lett., Vol. 83, No. 19, 10 November 2003
Lyapin et al.
3905
1
2
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the 2D polymers of C . On the other hand, it is well known
that graphite is much more compressible along the ͑002͒.
That is, in the presence of an additional uniaxial pressure
component along the Z axis, the orientation of clusters with
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(
1) (1)
(2) (2)
ratio (I /I )/(IZ /I ) provides a good evaluation for
(
Z
X
X
2
N /N ) , where N and N are the fraction of the graphite-
Z X Z X
like clusters with the graphene sheets perpendicular to Z and
X, respectively. In the double ratio, the superscripts denote
the numbers of peaks and the subscripts denote the scattering
vector directions. The N /N ratio estimated in this way
12
13
Z
X
correlates linearly with the elastic anisotropy for the longitu-
dinal sound velocities in Fig. 2͑c͒.
14
Summarizing, we have shown that nonhydrostatic pres-
sure is indeed a powerful tool for the preparation of aniso-
tropic carbon structures. The predominant orientation of the
polymerized planes in 2D polymerized C60 phases can serve
as a signature of an additional uniaxial pressure component.
15
16
17
2
In contrast, the formation of anisotropic graphite-type (sp )
͑
1999͒.
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components. In this case, the elastic anisotropy can be oppo-
site to that observed for the 2D polymerized C60 phases, but
it still correlates with the structural texture.
18
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The work was supported by the Russian Foundation for
Basic Research ͑Project No. 01-02-16557͒, INTAS ͑Project
No. 00-807͒, and NATO ͑Project No. PST.CLG.979346͒.
21
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1