Journal of
MATERIALS RESEARCH
Behavior of carbon nanotubes under high pressure and
high temperature
D.S. Tang, L.C. Chen, L.J. Wang, L.F. Sun, Z.Q. Liu, G. Wang, W.Y. Zhou, and S.S. Xiea)
Institute of Physics & Center of Condensed Matter Physics, Chinese Academy of Sciences,
P.O. Box 603, Beijing 100080, People’s Republic of China
(Received 2 July 1999; accepted 8 November 1999)
The structural changes of carbon nanotubes induced by high pressure and high
temperature were investigated by means of x-ray diffraction, Raman scattering,
scanning electron microscopy, and transmission electron microscopy. It is shown that,
with increasing pressure and temperature, the lattice constant d002 of tubes shortens,
and then tubes collapse into tapelike ones; at the same time the C–C bonds at high
curvature break, which lead the tapelike tubes to break into graphite sheets as
diamond crystallization centers. Compared with graphite, the diamond particles from
carbon nanotubes have many defects as the trace of tubes.
I. INTRODUCTION
high temperature reveals that the tubes first become tapes
and then graphitelike sheets as nuclei of diamond grow-
ing into diamond particles.
Since their discovery in 1991,1 carbon nanotubes have
attracted more and more interest for their unique mor-
phology and exceptionally physical and chemical prop-
erties.2–6 Theoretical studies of carbon nanotubes suggest
that their properties depend sensitively on their morphol-
ogy and structure.7–9 Therefore high pressure, which can
vary the interatomic distance of substance and thus
change its phase transition, was employed as an impor-
tant probe of the relation between the structure and the
property of carbon nanotubes. On the basis of graphite,
the transformation from carbon nanotubes to diamond
under high pressure and high temperature was realized
already,10,11 but the behavior of carbon nanotubes under
high pressure and high temperature is not clear yet even
though much experimental work has been done in this
aspect. For example, Zhou et al.12 studied defects in
carbon nanotubes through the average radial compress-
II. EXPERIMENTAL
In our experiments, multiwalled carbon nanotubes,
loosely entangled and most highly graphitized, were pre-
pared by modified arc discharge.15 The subsequent pu-
rification by the oxidizing process made the carbon
nanotubes free of contaminating nanoparticles and amor-
phous carbon [Fig. 3(a)]. The high pressure was created
by a 600-ton oil pressure machine, and the pressure-
transmitting medium was pyrophyllite. The samples were
indirectly heated by the electrical current through a
graphite furnace. As insulator, two BN sample cells
(4-mm diameter) were put into the graphite furnace. In
one of the BN sample cell carbon nanotubes (about
10 mg) were loaded, and in the other BN sample cell
graphite sample was loaded for comparing. The two
samples were covered with a piece of nickel-base alloy as
catalyst. After that, the sample was heated for several
seconds at the desired temperature under a certain pres-
sure, and then temperature was decreased and pressure
released to ambience in 1 min. The structural changes
were characterized by x-ray diffraction, Raman scatter-
ing, scanning electron microscopy (SEM), and transmis-
sion electron microscopy (TEM).
ibility calculated from the pressure-induced shift in d002
.
Zhang et al.13 investigated the thermal stability of carbon
nanotubes under 5.5 GPa. Zhu et al.14 investigated the
structural change of carbon nanotubes under shock
waves. In this paper, we investigate the behavior of car-
bon nanotubes under high pressure (up to 7.0 GPa) and
high temperature (up to 1800 °C) by means of x-ray
diffraction, Raman scattering, scanning electron micros-
copy, and transmission electron microscopy. The struc-
tural change of the sample induced by high pressure and
III. RESULTS AND DISCUSSION
The x-ray diffraction spectra of the pristine material
(purified carbon nanotubes) [Fig. 1(a)] and the samples
under the different pressure and temperature [Figs. 1(b)
a)Address all correspondence to this author.
e-mail: ssxie@aphy.iphy.ac.cn
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J. Mater. Res., Vol. 15, No. 2, Feb 2000
© 2000 Materials Research Society
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