Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen
The heat capacity Cm of polycrystalline fullerite C₆₀ doped with nitrogen has been measured in the temperature interval 2–13 K. The contributions to the heat capacity from translational lattice vibrations (Debye contribution), orientational vibrations of the C₆₀ molecules (Einstein contribution),...
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irk-123456789-1207852017-06-14T03:04:15Z Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen Gurevich, A.M. Terekhov, A.V. Kondrashev, D.S. Dolbin, A.V. Cassidy, D. Gadd, G.E. Moricca, S. Sundqvist, B. Кpаткие сообщения The heat capacity Cm of polycrystalline fullerite C₆₀ doped with nitrogen has been measured in the temperature interval 2–13 K. The contributions to the heat capacity from translational lattice vibrations (Debye contribution), orientational vibrations of the C₆₀ molecules (Einstein contribution), and from the motion of the N₂ molecules in the octahedral cavities of the C₆₀ lattice have been estimated. However, we could not find (beyond the experimental error limits) any indications of the first-order phase transformation that had been detected earlier in the dilatometric investigation of the orientational N₂–C₆₀ glass. A possible explanation of this fact is proposed. 2006 Article Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen / A.M. Gurevich, A.V. Terekhov, D.S. Kondrashev, A.V. Dolbin, D. Cassidy, G.E. Gadd, S. Moricca, B. Sundqvist // Физика низких температур. — 2006. — Т. 32, № 10. — С. 1275–1277. — Бібліогр.: 12 назв. — англ. 0132-6414 PACS: 74.70.Wz http://dspace.nbuv.gov.ua/handle/123456789/120785 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
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Кpаткие сообщения Кpаткие сообщения |
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Кpаткие сообщения Кpаткие сообщения Gurevich, A.M. Terekhov, A.V. Kondrashev, D.S. Dolbin, A.V. Cassidy, D. Gadd, G.E. Moricca, S. Sundqvist, B. Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen Физика низких температур |
| description |
The heat capacity Cm of polycrystalline fullerite C₆₀ doped with nitrogen has been measured in
the temperature interval 2–13 K. The contributions to the heat capacity from translational lattice
vibrations (Debye contribution), orientational vibrations of the C₆₀ molecules (Einstein contribution),
and from the motion of the N₂ molecules in the octahedral cavities of the C₆₀ lattice have
been estimated. However, we could not find (beyond the experimental error limits) any indications
of the first-order phase transformation that had been detected earlier in the dilatometric investigation
of the orientational N₂–C₆₀ glass. A possible explanation of this fact is proposed. |
| format |
Article |
| author |
Gurevich, A.M. Terekhov, A.V. Kondrashev, D.S. Dolbin, A.V. Cassidy, D. Gadd, G.E. Moricca, S. Sundqvist, B. |
| author_facet |
Gurevich, A.M. Terekhov, A.V. Kondrashev, D.S. Dolbin, A.V. Cassidy, D. Gadd, G.E. Moricca, S. Sundqvist, B. |
| author_sort |
Gurevich, A.M. |
| title |
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen |
| title_short |
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen |
| title_full |
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen |
| title_fullStr |
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen |
| title_full_unstemmed |
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen |
| title_sort |
low-temperature heat capacity of fullerite c₆₀ doped with nitrogen |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2006 |
| topic_facet |
Кpаткие сообщения |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/120785 |
| citation_txt |
Low-temperature heat capacity of fullerite C₆₀ doped with nitrogen / A.M. Gurevich, A.V. Terekhov, D.S. Kondrashev, A.V. Dolbin, D. Cassidy, G.E. Gadd, S. Moricca, B. Sundqvist // Физика низких температур. — 2006. — Т. 32, № 10. — С. 1275–1277. — Бібліогр.: 12 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
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2025-07-08T18:34:28Z |
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| fulltext |
Fizika Nizkikh Temperatur, 2006, v. 32, No. 10, p. 1275–1277
Short Notes
Low-temperature heat capacity of fullerite C60 doped with
nitrogen
A.M. Gurevich1, A.V. Terekhov1, D.S. Kondrashev1, A.V. Dolbin1,
D. Cassidy2, G.E. Gadd2, S. Moricca2, and B. Sundqvist3
1 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: dolbin@ilt.kharkov.ua
2 Australian Nuclear Science & Technology Organisation, Menai, NSW 2234, Australia
3 Department of Physics, Umea University, SE-901 87 Umea, Sweden
Received January 23, 2006, revised March 2, 2006
The heat capacity Cm of polycrystalline fullerite C60 doped with nitrogen has been measured in
the temperature interval 2–13 K. The contributions to the heat capacity from translational lattice
vibrations (Debye contribution), orientational vibrations of the C60 molecules (Einstein contribu-
tion), and from the motion of the N2 molecules in the octahedral cavities of the C60 lattice have
been estimated. However, we could not find (beyond the experimental error limits) any indica-
tions of the first-order phase transformation that had been detected earlier in the dilatometric in-
vestigation of the orientational N2–C60 glass. A possible explanation of this fact is proposed.
PACS: 74.70.Wz
Keywords: heat capacity, doped fullerite, nitrogen, impurity effect.
The doping of fullerites can affect their properties
significantly and thus extend their applications. The
impurity effect upon the properties of C60 has been
studied most extensively. In particular, the effects of
some gases (He, H2, D2, Ne, Ar, Kr, Xe, N2) upon the
thermal expansion and the structure of C60 at low
temperatures have been studied in sufficient detail
[1–3]. The most interesting results include in particu-
lar the detection of the first-order phase transition
stimulated by the gas impurities in the orientational
C60 glass [2,3]. Unfortunately, until now the heat ca-
pacity of the gas mixtures in fullerites has escaped the
attention of researchers. However, it is interesting to
know how the dissolved gases influence the heat ca-
pacity of C60 or how the first-order phase transition in
the glass manifests itself in the behavior of the heat
capacity. This knowledge is very important, too, be-
cause it is practically impossible to avoid contamina-
tion of C60 with air gases. We think that it is reason-
able to start investigation of the low-temperature heat
capacity of the gases dissolved in fullerites with a
N2–C60 solution because nitrogen is the main constitu-
ent of air. This is the basic objective of this study.
At room temperature C60 has a fcc lattice with one
octahedral and two tetrahedral interstitial cavities per
C60 molecule. The octahedral cavities are sufficiently
large in size (4.14 � [4]) to house molecules of many
gas impurities, including, for example, N2 molecules,
with a gas-kinetic diameter � = 3.7 � [5].
The sample was prepared from high-purity (99,99%)
C60 powder with average grain size � 100 mm (SES,
USA). First, the powder was intercalated with N2 and
then compacted. The intercalation was performed at
the Australian Nuclear Science and Technology Or-
ganization (ANSTO, Australia) under conditions of
P � 200 MPa, T = 575 �C and t = 36 h. The intercala-
tion technique is described in [6]. The thermal
gravimetric analysis results (ANSTO) showed that the
octahedral cavities of C60 were filled with N2 to prac-
tically 100%. The N2-intercalated C60 powder was
© A.M. Gurevich, A.V. Terekhov, D.S. Kondrashev, A.V. Dolbin, D. Cassidy, G.E. Gadd, S. Moricca, and B. Sundqvist, 2006
compacted at Umea University, Sweden, by the tech-
nique described in [1]. The investigation was started
twelve months after preparation of the sample. As a
result, according to x-ray analysis, the N2 concentra-
tion decreased to 20% [7].
The heat capacity of the C60 sample intercalated
with N2 was measured by the method of absolute calo-
rimetry in the interval 2–13 K. The calorimetric cell
was a rectangular copper-foil plate with a germanium
resistance thermometer and a film heater (R = 100 �)
fixed on it. The sample, with a mass of 0.3215 g, was
mounted on the free side of the plate, covered with a
thin layer of vacuum grease. The mass of the calori-
metric cell without a sample was 1.081 g. The heat ca-
pacity of the cell was measured separately. The mea-
surement error in the heat capacity of the sample was
3–7% (depending on the temperature interval).
The sample was cooled down to liquid helium tem-
perature by cold conduction through the wires (with-
out using helium gas as heat exchanging gas) in va-
cuum 10–2 Torr at room temperature and 10–6 Torr at
4.2 K. The heat capacity was measured in several se-
ries (Fig. 1).
The cooling to helium temperature took 24 hours.
Then the heat capacity of the calorimetric cell with
the sample was measured in a stepwise heating proce-
dure.
We described the temperature dependence of the
heat capacity using the following simplified scheme.
The heat capacity measured in the interval of experi-
mental temperatures was considered taking into ac-
count the contributions from all types of motion: the
Debye contribution, due to translational fullerite lat-
tice vibrations and the Einstein contributions, due to
orientational vibrations of the C60 molecules and the
influence of the N2 impurity molecules. The experi-
mental results are described fairly well using a Debye
term with the characteristic temperature �D = 45 K
and two Einstein terms with �E1 = 37 K and �E2 =
= 53 K (Fig. 2). The most reliable value for pure C60
is �D = 54 K in [1,8]. It is quite reasonable that our
�D is lower because (i) the intercalation with N2 in-
creases the molar volume of the C60 crystal and (ii)
the added impurity increases the effective molar
weight of the system.
Our model ignores two other contributions to the
heat capacity. One of them is the linear contribution
to the heat capacity of glasses. It can be responsible
for the discrepancy between the experimental and cal-
culated data at the lowest temperatures of the experi-
ment. The intramolecular vibrations of C60 molecules
also contribute to the heat capacity of C60. Their con-
tribution may account for the excess of the experimen-
tal values over the calculated ones in the high-temper-
ature region of our investigation.
It is known from the literature [1–3,9] that the
temperature dependence of the thermal expansion of
C60 intercalated with some gases at the temperatures
of liquid helium and nitrogen has a hysteresis. Adia-
batic calorimetry precludes measurement of the heat
capacity at decreasing temperature. However, a hys-
teresis can appear in heat capacity measurement even
on heating provided that the thermal prehistory of the
sample and the kinetic parameters of the experiment
are modified. To detect a hysteresis, the measurement
series were made at different starting temperatures
and with different rates of heating to the starting tem-
perature. The temperature interval («step») of mea-
surement was also varied. The sample was cycled at a
certain pre-assigned temperature. In this case the heat
capacity of the sample was measured at temperature
T1. The sample was then cooled down by 1–2 degrees
to T2 and the heat capacity was measured at T2.
1276 Fizika Nizkikh Temperatur, 2006, v. 32, No. 10
A.M. Gurevich et al.
2 4 6 8 10 120
5
10
15
20
T,K
C
,J
/m
o
l·K
Fig. 1. Molar heat capacity of polycrystalline C60 doped
with N2. The measurement series are indicated by different
symbols.
0 40 80 120 160
0,5
1,0
1,5
5 15 25
0,2
0,4
0,6
T , K2 2
T , K2 2
C
/T
,J
/m
o
l·K
m
2
C
/T
, J
/m
o
l·K
m
2
Fig. 2. Calculated and measured temperature dependences
of molar heat capacity of polycrystal C60 doped with N2:
measured N2–C60 heat capacity data (�); calculated
N2–C60 heat capacity (curve).
Finally, the sample was heated and the heat capacity
was measured at T1 again.
The measured heat capacities are within the limits
determined by the experimental error. The data ob-
tained suggest that the heat capacity of the N2–C60
system is insensitive to the processes provoking the
hysteresis effect. This may be due to the fact that, ac-
cording to [1,2], the hysteresis is caused by a first-or-
der phase transition between the orientational glasses
based on gas-doped fullerite. However, the difference
between the molar volumes of the phases in the tem-
perature interval 2–24 K is only 0.02% [1]. In this
case the transition-related change in the heat capacity
can be smaller than the experimental error. It should
be remembered that the phase transition in glasses
does not proceed at a constant temperature; it occurs
over a rather wide temperature interval. At the same
time the phase transformation is clearly indicated by a
change in the linear expansion coefficient [1,2]. The
reason may be that that the phase transition consid-
ered above is a tunnel transition during which the
change in the volume expansion coefficient can be sev-
eral orders of magnitude larger than the relative
change in the heat capacity [10]. It correlates well
with the very high Gruniesen coefficients in tunnel en-
ergy spectra [11,12].
To conclude, we emphasize that this study is the
first attempt to estimate the effect of gas impurities
upon the heat capacity of C60 and to find out the pos-
sibilities of further research in this direction. Since the
molecules of gas impurities have small sizes and
masses, we can hardly expect a significant impact of
the dissolved gas upon the heat capacity of C60 at tem-
peratures far from the phase transition interval. Ne-
vertheless, the increase in the heat capacity of C60 at
low temperatures observed after introduction of 20%
N2 exceeds considerably (by approximately 15%) the
effect that might be caused by the impurity-induced
change in the molar volume and the effective mass of
C60.
Our attempt to reveal the effect of the phase transi-
tion on the heat capacity in the orientational glass
N2–C60 has gone unrewarded.
It is evident that further investigations should be
made on solutions with higher concentrations of gas
impurities in which the molecules have larger sizes
and masses. With these conditions met, both the im-
purity contribution and the effect produced by the
phase transition are expected to increase appreciably.
It is also necessary to improve the technique of calori-
metric measurement, in particular, to ensure the possi-
bility of long-term maintenance of the solution sam-
ples at a constant temperature. We are planning
further investigations to pursue this goal.
We wish to thank V.G. Manzhelii and M.I. Ba-
gatskii for helpful participation in a discussion of the
results.
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Low temperature heat capacity of fullerite C60 doped with nitrogen
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