Argon effect on thermal expansion of fullerite C₆₀
The linear thermal expansion of compacted Ar-doped fullerite C₆₀(ArxC₆₀) is investigated at 2-12 K using dilatometric method. The thermal expansion of ArxC₆₀ was also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in the considerable change of t...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2001
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| Цитувати: | Argon effect on thermal expansion of fullerite C₆₀ / A.N. Aleksandrovskii , V.G. Gavrilko , V.B. Esel`son , V.G. Manzhelii, B.G. Udovidchenko , V.P. Maletskiy, B. Sundqvist // Физика низких температур. — 2001. — Т. 27, № 3. — С. 333-335. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1300042018-02-04T03:03:29Z Argon effect on thermal expansion of fullerite C₆₀ Aleksandrovskii, A.N. Gavrilko, V.G. Esel`son, V.B. Manzhelii, V.G. Udovidchenko, B.G. Maletskiy, V.P. Sundqvist, B. Письма pедактоpу The linear thermal expansion of compacted Ar-doped fullerite C₆₀(ArxC₆₀) is investigated at 2-12 K using dilatometric method. The thermal expansion of ArxC₆₀ was also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in the considerable change of the temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is proposed. 2001 Article Argon effect on thermal expansion of fullerite C₆₀ / A.N. Aleksandrovskii , V.G. Gavrilko , V.B. Esel`son , V.G. Manzhelii, B.G. Udovidchenko , V.P. Maletskiy, B. Sundqvist // Физика низких температур. — 2001. — Т. 27, № 3. — С. 333-335. — Бібліогр.: 11 назв. — англ. 0132-6414 PACS: 74.70.Wz http://dspace.nbuv.gov.ua/handle/123456789/130004 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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English |
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Письма pедактоpу Письма pедактоpу |
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Письма pедактоpу Письма pедактоpу Aleksandrovskii, A.N. Gavrilko, V.G. Esel`son, V.B. Manzhelii, V.G. Udovidchenko, B.G. Maletskiy, V.P. Sundqvist, B. Argon effect on thermal expansion of fullerite C₆₀ Физика низких температур |
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The linear thermal expansion of compacted Ar-doped fullerite C₆₀(ArxC₆₀) is investigated at 2-12 K using dilatometric method. The thermal expansion of ArxC₆₀ was also studied after partial desaturation of argon from fullerite. It is revealed that argon doping resulted in the considerable change of the temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is proposed. |
| format |
Article |
| author |
Aleksandrovskii, A.N. Gavrilko, V.G. Esel`son, V.B. Manzhelii, V.G. Udovidchenko, B.G. Maletskiy, V.P. Sundqvist, B. |
| author_facet |
Aleksandrovskii, A.N. Gavrilko, V.G. Esel`son, V.B. Manzhelii, V.G. Udovidchenko, B.G. Maletskiy, V.P. Sundqvist, B. |
| author_sort |
Aleksandrovskii, A.N. |
| title |
Argon effect on thermal expansion of fullerite C₆₀ |
| title_short |
Argon effect on thermal expansion of fullerite C₆₀ |
| title_full |
Argon effect on thermal expansion of fullerite C₆₀ |
| title_fullStr |
Argon effect on thermal expansion of fullerite C₆₀ |
| title_full_unstemmed |
Argon effect on thermal expansion of fullerite C₆₀ |
| title_sort |
argon effect on thermal expansion of fullerite c₆₀ |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2001 |
| topic_facet |
Письма pедактоpу |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/130004 |
| citation_txt |
Argon effect on thermal expansion of fullerite C₆₀ / A.N. Aleksandrovskii , V.G. Gavrilko , V.B. Esel`son , V.G. Manzhelii, B.G. Udovidchenko , V.P. Maletskiy, B. Sundqvist // Физика низких температур. — 2001. — Т. 27, № 3. — С. 333-335. — Бібліогр.: 11 назв. — англ. |
| series |
Физика низких температур |
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2025-07-09T12:41:12Z |
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| fulltext |
Fizika Nizkikh Temperatur, 2001, v. 27, No. 3, p. 333–335Aleksan dro vskii A. N., Ga vr ilko V . G., Ese l’ son V. B., Manzhelii V . G., Su ndqvist B., Udovidche nko B. G., and Maletskiy V. P.Ar go n effe ct on th erm al expan sio n of fuller it e C6 0 at helium t emp era tur esAleksa ndr ovskii A. N. , Gavrilko V. G., E sel’son V. B., Manzhe lii V. G., Sundq vist B., Udovidch enko B. G., an d Malet skiy V. P.A rg on eff ect on t her mal expa nsion of fu ller ite C60 at he lium tem per atur es
Letters to the Editor
Argon effect on thermal expansion of fullerite C60
at helium temperatures
A. N. Aleksandrovskii1, V. G. Gavrilko1, V. B. Esel’son1, V. G. Manzhelii1,
B. Sundqvist2, B. G. Udovidchenko1, and V. P. Maletskiy1
1B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine,
Lenin Ave. 47, 61164, Kharkov, Ukraine
2 Umea University, Department of Experimental Physics, 90187, Umea, Sweden
Received December 26, 2000
The linear thermal expansion of compacted Ar-doped fullerite C
60 (Ar
x
C
60
) is investigated at 2–12 K
using dilatometric method. The thermal expansion of ArxC60 was also studied after partial desaturation
of argon from fullerite. It is revealed that argon doping resulted in the considerable change of the
temperature dependence of the thermal expansion of fullerite. An explanation of the observed effects is
proposed.
PACS: 74.70.Wz
A. N . Aleksandrovskii et al.
We have already reported the detection and
investigation of a negative linear thermal expansion
coefficient α of fullerite C60 at helium tempera-
tures [1,2]. The effect was tentatively attributed to
tunneling transitions between energetically equiva-
lent orientations of C60 molecules. To test this
assumption, we have studied the thermal expansion
of Ar-doped C60 at liquid helium temperatures. The
results of these studies are presented in this commu-
nication. In a fullerite crystal each C60 molecule is
associated with two tetrahedral and one octahedral
interstitial cavities [3] whose average linear dimen-
sions are about 2.2 A° and 4.2 A° , respectively [4].
According to x-ray [5] and neutron diffraction [6, 8]
data, the Ar atoms with the gas-kinetic diameter
3.405 A° [7] occupy only the octahedral cavities. It
should also be noted that at 15 K the lattice pa-
rameter of a saturated ArxC60 solution is 0.006 A°
smaller than that of fullerite [6]. We assumed that
the Ar atoms occupying the octahedral interstices
would increase the potential barrier impeding rota-
tion of the C60 molecules and thus diminish the
probability of rotational tunnel transitions and con-
sequently the tunneling splitting of the ground
state of the molecules [2]. If this assumption is
correct, the total negative thermal expansion
∫ α dT should decrease and the region of negative
expansion will shift towards lower temperatures
after doping.
An Ar-doped C60 sample was studied at 2–12 K
using a high-sensitivity capacitance dilatometer [9]
and with the same procedure as was applied to pure
C60 earlier [1,2]. The sample was prepared by com-
pacting high-purity (not worse than 99.98% C60)
powder under about 1 kbar. The grain sizes were
0.1–0.3 mm. The resulting C60 sample was a cylin-
der 9 mm high and 10 mm in diameter. The thermal
expansion coefficient along the cylinder axis was
first measured at 2–12 K before doping. The evacu-
ated sealed measuring cell with the sample has been
warmed to room temperature and filled with argon
under atmospheric pressure. The doping lasted for
19 days.
When the doping process was completed, the
Ar-filled measuring cell with the sample was slowly
cooled to helium temperatures. In this case both the
phase transitions of C60 (at 260 and 90 K) occurred
in an Ar atmosphere. Figure 1 shows the measured
coefficients before (curve 1) and after (curve 2)
Ar-doping. It is seen that the doping not only leads
to the expected decrease in the negative thermal
expansion and its shift towards lower temperatures
© A. N. Aleksandrovskii, V. G. Gavrilko, V. B. Esel’son, V. G. Manzhelii, B. Sundqvist, B. G. Udovidchenko, and V. P. Maletskiy, 2001
but that it also reduces strongly the (positive)
thermal expansion coefficient above 5.5 K.
It seems natural to assume that the Ar-induced
increase in the barrier impeding rotational motion
of the C60 molecules should also enhance the angu-
lar dependence of the non-central forces acting upon
the C60 molecules. As a result, the frequencies of
the orientational oscillations of the molecules
should increase and hence the normal (positive)
thermal expansion coefficient dependent on these
oscillations should decrease. This is what we ob-
served experimentally at T > 5.5 K. The experi-
mental results can thus be explained qualitatively
proceeding from the assumption that the atomic Ar
impurity introduced to the octahedral interstices of
C60 suppresses the splitting of the ground state of
the C60 molecules and modifies the orientational
oscillation spectrum of the molecules.
It appears that dissolved Ar atoms influence very
strongly the thermal expansion even though they
are able to move quite freely inside the octahedral
lattice interstices. We should also bear in mind that
in our experiment the Ar atoms occupy only a part
of the octahedral interstices. We did not estimate
the quantity of the dissolved Ar. According to
Morosin et al. [10], neon occupies only 21% of the
octahedral interstices under identical conditions
(room temperatures, atmospheric pressure). Taking
into account that in a simple cubic lattice each of
C60 molecules is surrounded by six octahedral inter-
stices, the 21% occupancy implies that with ran-
domly distributed impurity atoms about 75% of the
C60 molecules have Ar atoms nearby. However,
because the Ar atoms are larger than Ne atoms, this
number must be considered an upper limit of occu-
pancy only.
Another important consideration here is that we
believe that only a small fraction of the C60 mole-
cules (the so-called «defects») for which the rota-
tion-impending barrier Uϕ is quite low contributes
to the negative thermal expansion of fullerite [2].
Correspondingly the doping-induced change in the
negative thermal expansion is determined only by
the Ar atoms neighboring these «defects». At the
same time, the positive thermal expansion is af-
fected by all the dissolved Ar atoms.
To obtain more information, we studied how the
thermal expansion coefficient changed when the
doping atoms were removed from the sample. For
this purpose, the measuring cell with the sample
was warmed to room temperature and evacuated to
1⋅10−3 mm Hg. The gas evacuation at room tem-
perature lasted for 3 days. The thermal expansion
was then measured at low temperatures. The results
are shown in Fig. 1 (curve 3). It is seen that the
thermal expansion coefficient changes only slightly
above 5 K but below 3.5 K the negative thermal
expansion again has the minimum typical for un-
doped C60 . The measuring cell with the sample was
warmed again to room temperature and gas evacu-
ation was continued for 42 days. The thermal ex-
pansion coefficient was then measured with the
results shown in Fig. 1 (curve 4). Note, in particu-
lar, that after a total of 45 days evacuation of argon
the «high-temperature» part of the thermal expan-
sion coefficient was restored completely. The nega-
tive thermal expansion in the range 2.5–5 K, how-
ever, still differed from that of the initial pure
sample.
This can be accounted for assuming the follow-
ing. The octahedral voids adjacent to defects, i.e.,
C60 molecules with low Uϕ barriers, form deeper
potential wells for the impurity atoms than the
regular octahedral interstices do. It is therefore
more difficult to remove the impurities from these
near-defect regions, and the residual impurities con-
centrated around defects are precisely those respon-
sible for the negative thermal expansion of fullerite.
There is also another fact supporting this assump-
tion. The thermal expansion coefficients α of all our
C60 samples, both used in Refs. 1, 2 and in this
study, agree quite well above 5 K but they differ
considerably in the temperature region where α is
negative. These samples were prepared under diffe-
rent conditions and vary in quality and in the
amount of residual impurities.
The proposed qualitative explanation of the ef-
fect observed cannot replace a consistent theoretical
Fig. 1. Temperature dependences of the thermal expansion of
compacted fulletite C60 : pure fullerite before doping (1); Ar-
doped fullerite (2); fullerite after evacuation of Ar for 3 days
(3) and for 45 days (4).
A. N. Aleksandrovskii et al.
334 Fizika Nizkikh Temperatur, 2001, v. 27, No. 3
interpretation. Several interesting ideas have been
published to date, which are concerned with a
tentative mechanism of the negative thermal expan-
sion of molecular crystals [11]. In the case of
fullerite, we decide in favor of our explanation since
it accounts for the unusually high Gruneisen coeffi-
cients, which were observed experimentally.
We wish to thank Yu. A. Freiman, V. M. Lok-
tev, V. D. Natsik, A. I. Prokhvatilov, and M. A.
Strzhemechny for participation in the discussion of
the results.
The authors are indebted to the Science and
Technology Center of Ukraine and the Royal Aca-
demy of Sweden for support.
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Argon effect on thermal expansion of fullerite C60 at helium temperatures
Fizika Nizkikh Temperatur, 2001, v. 27, No. 3 335
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