Process of intercalation of C₆₀ with molecular hydrogen from XRD data
The process of normal hydrogen infusion into a C₆₀ powder at 1 bar and room temperature was monitored using x-ray diffraction. The effect of the intercalation on the lattice proved to be rather weak: the volume expansion upon complete saturation does not exceed 0.13%. The characteristic saturation t...
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| Cite this: | Process of intercalation of C₆₀ with molecular hydrogen from XRD data / K.A. Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, M.A. Strzhemechny, E. Schafler, M. Zehetbauer // Физика низких температур. — 2009. — Т. 35, № 3. — С. 315-319 . — Бібліогр.: 25 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1170522025-06-03T16:26:43Z Process of intercalation of C₆₀ with molecular hydrogen from XRD data Yagotintsev, K.A. Stetsenko, Yu.E. Legchenkova, I.V. Prokhvatilov, A.I. Strzhemechny, M.A. Schafler, E. Zehetbauer, M. Динамика кристаллической решетки The process of normal hydrogen infusion into a C₆₀ powder at 1 bar and room temperature was monitored using x-ray diffraction. The effect of the intercalation on the lattice proved to be rather weak: the volume expansion upon complete saturation does not exceed 0.13%. The characteristic saturation time was found to be 320 h; the corresponding diffusion coefficient amounts to (2.8 ± 0.8)·10⁻¹⁴ cm²/s. The integrated reflection intensity calculations for completely saturated sample suggest that only octahedral voids are filled under the conditions of experiment. The effect of complete saturation on the rotational subsystem of the C₆₀ fullerite is rather weak: the orientational phase transition shifts by 6 to 7 K to lower temperatures; no essential hysteresis is noticeable. The dopant shows reluctance to leave the sample under a vacuum of 10⁻³ Torr at room temperature. The authors are grateful to P.V. Zinoviev for critical reading of the manuscript. This work was supported by the Ukrainian-Austrian grant M/140-2007. 2009 Article Process of intercalation of C₆₀ with molecular hydrogen from XRD data / K.A. Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, M.A. Strzhemechny, E. Schafler, M. Zehetbauer // Физика низких температур. — 2009. — Т. 35, № 3. — С. 315-319 . — Бібліогр.: 25 назв. — англ. 0132-6414 PACS: 61.05.cp, 61.48.–c, 61.72.J-, 61.72.U- https://nasplib.isofts.kiev.ua/handle/123456789/117052 en Физика низких температур application/pdf Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Динамика кристаллической решетки Динамика кристаллической решетки |
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Динамика кристаллической решетки Динамика кристаллической решетки Yagotintsev, K.A. Stetsenko, Yu.E. Legchenkova, I.V. Prokhvatilov, A.I. Strzhemechny, M.A. Schafler, E. Zehetbauer, M. Process of intercalation of C₆₀ with molecular hydrogen from XRD data Физика низких температур |
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The process of normal hydrogen infusion into a C₆₀ powder at 1 bar and room temperature was monitored using x-ray diffraction. The effect of the intercalation on the lattice proved to be rather weak: the volume expansion upon complete saturation does not exceed 0.13%. The characteristic saturation time was found to be 320 h; the corresponding diffusion coefficient amounts to (2.8 ± 0.8)·10⁻¹⁴ cm²/s. The integrated reflection intensity calculations for completely saturated sample suggest that only octahedral voids are filled under the conditions of experiment. The effect of complete saturation on the rotational subsystem of the C₆₀ fullerite is rather weak: the orientational phase transition shifts by 6 to 7 K to lower temperatures; no essential hysteresis is noticeable. The dopant shows reluctance to leave the sample under a vacuum of 10⁻³ Torr at room temperature. |
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Yagotintsev, K.A. Stetsenko, Yu.E. Legchenkova, I.V. Prokhvatilov, A.I. Strzhemechny, M.A. Schafler, E. Zehetbauer, M. |
| author_facet |
Yagotintsev, K.A. Stetsenko, Yu.E. Legchenkova, I.V. Prokhvatilov, A.I. Strzhemechny, M.A. Schafler, E. Zehetbauer, M. |
| author_sort |
Yagotintsev, K.A. |
| title |
Process of intercalation of C₆₀ with molecular hydrogen from XRD data |
| title_short |
Process of intercalation of C₆₀ with molecular hydrogen from XRD data |
| title_full |
Process of intercalation of C₆₀ with molecular hydrogen from XRD data |
| title_fullStr |
Process of intercalation of C₆₀ with molecular hydrogen from XRD data |
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Process of intercalation of C₆₀ with molecular hydrogen from XRD data |
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process of intercalation of c₆₀ with molecular hydrogen from xrd data |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Динамика кристаллической решетки |
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Process of intercalation of C₆₀ with molecular hydrogen from XRD data / K.A. Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, M.A. Strzhemechny, E. Schafler, M. Zehetbauer // Физика низких температур. — 2009. — Т. 35, № 3. — С. 315-319 . — Бібліогр.: 25 назв. — англ. |
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Физика низких температур |
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| fulltext |
Fizika Nizkikh Temperatur, 2009, v. 35, No. 3, p. 315–319
Process of intercalation of C60 with molecular hydrogen
from XRD data
K.A. Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, and
M.A. Strzhemechny
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: yagotintsev@ilt.kharkov.ua
E. Schafler and M. Zehetbauer
Physics of Nanostructured Materials Group, Physics Faculty, Vienna University
Bolttzmann Gasse 5, Vienna A-1090, Austria
Received November 18, 2008
The process of normal hydrogen infusion into a C60 powder at 1 bar and room temperature was moni-
tored using x-ray diffraction. The effect of the intercalation on the lattice proved to be rather weak: the vol-
ume expansion upon complete saturation does not exceed 0.13%. The characteristic saturation time was
found to be 320 h; the corresponding diffusion coefficient amounts to (2.8 ± 0.8)�10
–14
cm
2
/s. The integrated
reflection intensity calculations for completely saturated sample suggest that only octahedral voids are
filled under the conditions of experiment. The effect of complete saturation on the rotational subsystem of
the C60 fullerite is rather weak: the orientational phase transition shifts by 6 to 7 K to lower temperatures; no
essential hysteresis is noticeable. The dopant shows reluctance to leave the sample under a vacuum of 10
–3
Torr at room temperature.
PACS: 61.05.cp X-ray diffraction;
61.48.–c Structure of fullerenes and related hollow molecular clusters;
61.72.J- Point defects and defect clusters;
61.72.U- Doping and impurity implantation.
Keywords: fullerite C60, hydrogen doping, degassing, powder x-ray, diffusion.
Introduction
Fullerite C60 is still considered as a good candidate for
gas separation or efficient storage of molecular hydrogen
[1]. It is therefore necessary to understand the interaction
of H2 with carbon nanostructures of all types and the kinet-
ics of penetration of hydrogen into fullerite C60. At
elevated pressure hydrogen is known to easily diffuse into
the C60 lattice within two or three hours at room tempera-
ture [2,3]. At present, the spectrum of an isolated hydrogen
molecule trapped in an octahedral void is well known [4].
The fcc lattice of fullerite C60 contains quite large interstitial
octahedral (the size of about 2.3 �) and tetrahedral (the size
of about 1.1 �) voids, which, under certain conditions, al-
low filling with various atoms and molecules. Hydrogen in
tetrahedral sites has a higher ground state energy compared
to octahedral ones. Nonetheless the tetrahedral sites appear
to be important dynamically [3,5] when loading or evacuat-
ing C60. Intercalation brings about noticeable changes in the
structural and other physical properties of fullerite crystals
[3,6–9]. The orientational system is the most sensitive to in-
tercalation [8,10]: even the lattice symmetry can change
upon saturation [11].
There are solid grounds for the conclusion that loading
of hydrogen into C60 under not too severe conditions does
not entail chemical bonding of hydrogen with the carbon
atoms in buckyballs. Only at high temperatures (T > 620 K)
and pressures (P > 100 bar) hydrogen actively react with
C60 [12–14]. Low-temperature studies of C60 doped with
CO [15], NO [16], or H2 [17] also yielded evidence that
no chemical bonding was involved but a strong effect
of doping on the orientational glass state occurred. The
C60–H2 system was thoroughly studied using various tech-
© K.A. Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, M.A. Strzhemechny, E. Schafler, and M. Zehetbauer, 2009
niques (see the above references and others [2,18–21].
Based on the relevant experimental findings it has been
concluded that the low-temperature dynamics of H2 and D2
molecules in the fullerite lattice is of quantum nature and
the high-temperature mobility of these molecules is high
enough. It is commonly considered that, because of the
smaller dimensions of tetrahedral cavities, the hydrogen
molecules occupy predominantly octahedral voids and that
their interaction with the matrix particles becomes essen-
tial at sufficiently low (T � 100 K) temperatures.
The aim of this paper was to carry out powder x-ray
diffraction studies of the process of intercalation of C60
with normal hydrogen as well as the effect of this interca-
lation on the structural and thermodynamic (rotational
contribution) properties over a wide temperature interval
from 10 to 296 K in order to solve a few questions. First,
we planned to utilize accurate structural characteristics
(reflection widths and intensities) to better understand the
migration and dynamical behavior of the H2 interstitial in
the C60 lattice. Second, we needed to know details of the
temporal dependence of the saturation process at compar-
atively low pressures in order to have reliable grounds for
the assessment of the dopant concentration over the pow-
der crystallite volume, which is important for the correct
treatment of the ensuing photoluminescence experiments,
part of which have been published elsewhere [17].
Experimental
In our investigations we used a high purity (99.98%
Aldrich) polycrystalline fullerite C60. Two types of powder
samples were studied. Both were prepared from the same
rather large-grain material: one (type I) was a result of man-
ual grinding to an average grain size of about (1.8 ± 1.0) �;
the other (type II) was milled to smaller grain sizes. Pre-
liminary XRD characterization of type II samples showed
that they were polymerized to a substantial degree, most
likely because of the prolonged milling. Mild annealing of
these sample removed most of the features in the XRD pat-
terns but not completely. Detailed x-ray measurements re-
ported below have been carried out only on type I samples.
With the aim of preliminary degassing the samples
were kept for five days at 200 °C in a vacuum of about
10–3 Torr. Then the sample was placed at room tempera-
ture into the working chamber of a x-ray cryostat and was
kept there continuously at 1 bar for a quite long time. Dur-
ing the intercalation process, the powder sample was
XRD characterized, the time between successive takes
varying from 1 to 10 h initial stages to 100 h or more at
longer intercalation times. The saturation complete, the
structure characteristics of the saturated sample were
studied as a function of temperature, both under
cooldown and warmup. The temperature interval inclu-
ded the two critical points, viz., the orientational phase
transition at about 260 K and the orientational vitrifica-
tion point at � 95 K.
The x-ray studies were performed using an automated
DRON x-ray diffractometers with a nickel anode (� =
= 1.6591 �). The temperature was stabilized within the
whole 11 to 300 K range to ± 0.1 K. The characteristic lat-
tice parameter error was about 0.02% if the complete
x-ray pattern was recorded. High-accuracy measurements
of that type have been performed at 11 K and at room tem-
perature. The temperature dependence of the lattice pa-
rameter between these two reference points was evaluated
from the positions of the three most intensive reflections
(111), (220), and (311).
After the completely saturated sample was finally
characterized as described above, the intercalant was eva-
cuated from the fullerite lattice. To this end, the chamber
was pumped down to 10–3 Torr and the lattice parameter
was monitored in time until it came to a constant level.
During both saturation and degassing we determined the
widths and intensities of the above reference reflections,
which allowed us to make certain conclusions concerning
the diffusion process of H2 in crystalline C60.
Results and discussion
Our measurements of the lattice parameter a as a func-
tion of intercalation time showed that the properties of
this C60–H2 system differ substantially from those found
for He in C60. As C60 was kept at room temperature in the
hydrogen atmosphere, its lattice parameter a grew per-
ceptibly but little during the initial 200 h from 14.161 to
14.167 � and afterwards stayed virtually unchanged dur-
ing a very long period of up to 2000 h to within experi-
mental scatter. We also subjected an annealed type II sam-
ple to the same saturation procedure. The starting lattice
parameter was somewhat smaller than in the type-I sam-
ple; upon saturation during about 300 h the lattice param-
eter increment was below 0.002 �, which is barely above
the experimental error. The smaller intercalation-related
expansion of the type II sample can be due to the presence
of the polymeric bonds, which are known to cause a sharp
increase in the hardness and Young modulus [22].
We remind that the process of the intercalation of C60
with helium under the same conditions has two stages:
during the first stage it is octahedral voids that are filled
comparatively fast; the second, much slower stage corre-
sponds to the filling of tetrahedral voids with He atoms.
In the C60–H2 system the second stage is absent, which
suggests that hydrogen molecules do not penetrate into
tetrahedral voids, at least at the pressure of our experi-
ment (around 1 bar). Otherwise, the lattice must have re-
sponded with a much larger expansion. Since the satura-
tion in the case of hydrogen was completed at room
temperature and taking into consideration [5] that the mi-
gration over octahedral voids proceeds through tetrahe-
316 Fizika Nizkikh Temperatur, 2009, v. 35, No. 3
K.A.Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, M.A. Strzhemechny, E. Schafler, and M. Zehetbauer
dral cavities, it is clear that the intensive translational
motion of C60 molecules at 300 K allows a hydrogen mo-
lecule to occupy only momentarily a neighboring tetrahe-
dral site with subsequent jump to an octahedral void.
The second difference concerns the magnitude of the
intercalation-related C60 lattice expansion. With He [5],
the total expansion when octahedral voids are occupied to
the full (at the end of stage 1) is much larger (by a factor
of 3.5) compared to the case of hydrogen as intercalant. A
possible explanation can be ascribed to the larger diame-
ter of the H2 molecule, which deprives it freedom to move
in a gas-like fashion (as a He atom does) exerting a pres-
sure on the octahedral cage from within. This is more so,
considering a substantially stronger interaction between
C60 and H2 molecules.
In Fig. 1 we show the measured time dependence of the
lattice parameter increment (empty circles) normalized to
the maximum increment at complete saturation; the rele-
vant parameters are a0 = 14.161 � and ainf = 14.167 �. Ap-
plying of the diffusion theory in the spherical geometry ap-
proximation (solid curve in Fig. 1), similar to that
employed [5] for He–C60 system, we estimate the charac-
teristic time to be 320 h. Knowing the average grain size
(about 1.8 �) we calculate the diffusion coefficient of H2 in
C60 at room temperature to be D � (2.8 ± 0.8)�10–14 cm2/s,
which is only 2.7 slower than for He atoms at the same
conditions. The reason for that might be that as far as dif-
fusion is concerned the stronger C60–H2 interaction is
outbalanced by the lighter hydrogen mass.
The fact that the time dependence of the full widths at
half-maximum (FWHM) for the C60–H2 system (Fig. 2)
does not reveal a clear maximum, like in the C60–He sys-
tem, may be due to the insignificant lattice distortions in
the case of hydrogen that could entail a line broadening
detectable in our experiment.
In Fig. 3 we show the time dependence of the inte-
grated intensities of the same three reflections during the
initial stages of saturation; all three lines tend to become
weaker with progressing saturation. According to evalua-
tions similar to those for the C60–He system [5], lines
(111) and (220) were expected to weaken at complete sat-
uration by roughly 4% and 5% whereas line (311) was to
brighten by 6%, after which they must level off. As ex-
pected, during the initial stages of saturation the inte-
grated intensities of lines (111) and (200) went down by,
respectively, 4.4% and 5.2%. However, like in the case of
the C60–He system, the line (311) in Fig. 3 did not obey
our predictions: although the intensity change was 6.3%
but it diminished instead of growing. Nevertheless, these
findings allow us to conclude that the saturation of pow-
der was very close to complete. These inferences are at
variance with the conclusions of Aleksandrovskii et al.
[21] that a similar intercalation procedure results in a 12%
Process of intercalation of C60 with molecular hydrogen from XRD data
Fizika Nizkikh Temperatur, 2009, v. 35, No. 3 317
0 200 400 600 800
0
0.2
0.4
0.6
0.8
1.0
H in C2 60
Intercalation time, h
(a
–
a
)/
(a
–
a
)
0
in
f
0
Fig. 1. The reduced cubic lattice parameter increment as a func-
tion of the normal hydrogen intercalation time at a pressure of 1
bar and room temperature. The circles are experimental data, the
curve is the diffusion theory for spherical particles (see also text).
0 100 200 300 400 500
0.18
0.19
0.20
0.21
0.22
0.23
0.24
C – nH60 2
P = 1 bar, T = 293 K
(311)
(220)
Time, h
(111)
�
�
2
,
d
eg
Fig. 2. The FWHM of the three bright reflections as a function
of the hydrogen intercalation time.
0 100 200 300 400 500
2600
2800
3000
3200
3400
(111)
(220)
(311)
Time, h
In
te
n
si
ty
,
ar
b
.
u
n
it
s
Fig. 3. Variations of the integrated intensities of the three
bright reflections during intercalation.
occupancy. This striking discrepancy is most likely due to
the capital difference in the samples studied: our sample
was a loose set of separate small grains of a ten micron size
whereas the sample in the low-temperature thermal expan-
sion experiments [21] was a large block of compressed C60
of a few centimeters. Therefore, in the latter case the char-
acteristic diffusion time must be roughly (1 cm/ 1 �)2 times
longer than our value of 320 h and, thus, their estimated
occupancy of 12% does not seem unrealistic.
Stuffing crystalline C60 with hydrogen must affect
the intermolecular interactions and thermodynamic char-
acteristics. Usually, orientational transition points are
sensitive to various impurities. In order to establish
how intercalated hydrogen influences the processes of
orientational ordering and glassification, we studied the
temperature dependence of the lattice parameter of the ul-
timately saturated sample from 11 to 293 K both in the
cooldown and warmup regimes. These data are presented
in Fig. 4 together with our results for high-purity fullerite
C60 [23]. It should be noted that notwithstanding the very
small saturation-related expansion the orientational phase
transition is shifted appreciably (by 6 to 7 K) to lower
temperatures. The very phase transition is understandable
less acute than in ideal crystals owing to remaining irreg-
ularities of the distribution of the hydrogen molecules
over the volume of crystallites. As a result, the lattice pa-
rameter jump across the transition is understandably
smaller than in pure samples. At any temperature the lat-
tice parameter in saturated samples exceeds that in pure
C60; at room temperature the relative lattice parameter in-
crease is about 4.3�10–4, which is only twice the experi-
mental error.
Down to 130 K no clearly detectable hysteresis is
observed. At lower temperatures, close and below the
orientational glassification point, a hysteresis is clearly de-
tectable. This hysteresis, which is by far less pronounced
than with other neutral intercalants, especially Xe [24],
could be possibly due to the so called polyamorphic trans-
formations [25].
We also measured the temperature dependence of the
standard structure characteristics (widths and intensities)
for the three bright reflections in the completely saturated
sample. To speed up the procedure, only a short region
where the set of closely spaced reflections (220, 222, 311)
are situated, was recorded. From Fig. 5 one can see that
the integrated intensities do not change appreciably (only
due to changes brought about by thermal expansion); the
temperature dependence is rather smooth, if not for weak
phantom disturbances around the critical points. The
FWHM of the same reflections (Fig. 6) do not show large
anomalies. However, in the region of the transition to the
orientational glass state all traces reveal a surge which
suggests freezing-in of static strains in this disordered
state. These strains are not related with the presence of the
intercalant but appear owing to the (partial) disorder in
the mutual orientations of neighboring C60 molecules.
Degassing undertaken within the same procedure as in
the case with He [5] (evacuation in a vacuum of 10�3 Torr
at room temperature) showed that, unlike helium, hydro-
gen is very reluctant to leave C60. Even after more than 50
days the lattice parameter, though having somewhat di-
minished, remained above the value characteristic for
pure fullerite beyond experimental error. A similar effect
has been documented by Aleksandrovskii et al. [23] in
dilatometry experiments.
318 Fizika Nizkikh Temperatur, 2009, v. 35, No. 3
K.A.Yagotintsev, Yu.E. Stetsenko, I.V. Legchenkova, A.I. Prokhvatilov, M.A. Strzhemechny, E. Schafler, and M. Zehetbauer
0 50 100 150 200 250 300
14.04
14.06
14.08
14.10
14.12
14.14
14.16
14.18
Tg
TC
T, K
C + nH60 2
Fig. 4. Temperature dependence of the cubic lattice parameter
of C60 fullerite with octahedral voids completely occupied by
hydrogen molecules. The symbols (�) and (�) denote respec-
tively cooldown and warmup data; the solid line is for pure
C60 [23].
0 50 100 150 200 250 300
500
1000
1500
2000
2500
3000
(222)
(311)
(220)
T, K
In
te
n
si
ty
,
ar
b
.
u
n
it
s
Fig. 5. The integrated intensity of three closely spaced lines of
the saturated sample as a function of temperature.
Conclusions
The process of loading C60 with normal hydrogen at
room temperature and a pressure of 1 bar was studied by
monitoring the XRD characteristics (Bragg angles as well
as the intensities and widths of reflections). Our experi-
mental data together with integrated intensities calcula-
tions allowed us to conclude that only octahedral voids are
filled under the above conditions. The characteristic hy-
drogen infusion time was evaluated to be 320 h, which cor-
responds to the diffusion coefficient about 3�10–14 cm2/s.
The temperature dependence of the lattice parameter
of a completely saturated C60 powder sample show insig-
nificant changes compared to pristine C60; a 6–7 K shift
of the orientational transition point to lower tempera-
tures; at all temperatures the lattice parameter is slightly
higher than in pure samples (at room temperature the in-
tercalation-related volume expansion does not exceed
0.13%); no essential hysteresis was observed in the tem-
perature range studied.
The authors are grateful to P.V. Zinoviev for critical
reading of the manuscript. This work was supported by
the Ukrainian-Austrian grant M/140-2007.
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Process of intercalation of C60 with molecular hydrogen from XRD data
Fizika Nizkikh Temperatur, 2009, v. 35, No. 3 319
0 50 100 150 200 250 300
0.17
0.18
0.19
0.20
0.21
0.22
0.23
0.24
(222)
(311)
(220)
T, K
�
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2
,
d
eg
Fig. 6. The full widths at half-maximum as a function of temper-
ature for the three closely spaced lines of the saturated sample.
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