Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects
The kinetics of helium gas sorption by a C₆₀ powder and subsequent desorption of the ⁴He impurity from the saturated powder has been investigated in the temperature interval 2–292 K. Evidence is obtained that supports the existence of two stages in the temperature dependences of sorption and desorpt...
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irk-123456789-1175412017-05-25T03:03:28Z Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects Dolbin, A.V. Esel'son, V.B. Gavrilko, V.G. Manzhelii, V.G. Vinnikov, N.A. Popov, S.N. Наноструктуры при низких температурах The kinetics of helium gas sorption by a C₆₀ powder and subsequent desorption of the ⁴He impurity from the saturated powder has been investigated in the temperature interval 2–292 K. Evidence is obtained that supports the existence of two stages in the temperature dependences of sorption and desorption. The stages account for the different times taken by helium to occupy the octahedral and tetrahedral interstices in the C₆₀ lattice. The characteristic times of sorption and desorption coincide. It is found that the temperature dependences of the characteristic times of occupying the octahedral and tetrahedral interstices are nonmonotonic. As the temperature is lowered from 292 to 79.3 K, the characteristic times increase, which indicates a predominance of thermally activated diffusion of helium in C₆₀. On a further decrease to T = 10 K the characteristic times reduce over an order of magnitude. Below 8 K the characteristic times of sorption and desorption are temperature-independent. This suggests a tunnel character of ⁴He diffusion in C₆₀. 2010 Article Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects / A.V. Dolbin, V.B. Esel'son, V.G. Gavrilko, V.G. Manzhelii, N.A.Vinnikov, S.N. Popov // Физика низких температур. — 2010. — Т. 36, № 12. — С. 1352–1355. — Бібліогр.: 16 назв. — англ. 0132-6414 PACS: 68.43.Mn http://dspace.nbuv.gov.ua/handle/123456789/117541 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Наноструктуры при низких температурах Наноструктуры при низких температурах |
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Наноструктуры при низких температурах Наноструктуры при низких температурах Dolbin, A.V. Esel'son, V.B. Gavrilko, V.G. Manzhelii, V.G. Vinnikov, N.A. Popov, S.N. Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects Физика низких температур |
| description |
The kinetics of helium gas sorption by a C₆₀ powder and subsequent desorption of the ⁴He impurity from the saturated powder has been investigated in the temperature interval 2–292 K. Evidence is obtained that supports the existence of two stages in the temperature dependences of sorption and desorption. The stages account for the different times taken by helium to occupy the octahedral and tetrahedral interstices in the C₆₀ lattice. The characteristic times of sorption and desorption coincide. It is found that the temperature dependences of the characteristic times of occupying the octahedral and tetrahedral interstices are nonmonotonic. As the temperature is lowered from 292 to 79.3 K, the characteristic times increase, which indicates a predominance of thermally activated diffusion of helium in C₆₀. On a further decrease to T = 10 K the characteristic times reduce over an order of magnitude. Below 8 K the characteristic times of sorption and desorption are temperature-independent. This suggests a tunnel character of ⁴He diffusion in C₆₀. |
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Article |
| author |
Dolbin, A.V. Esel'son, V.B. Gavrilko, V.G. Manzhelii, V.G. Vinnikov, N.A. Popov, S.N. |
| author_facet |
Dolbin, A.V. Esel'son, V.B. Gavrilko, V.G. Manzhelii, V.G. Vinnikov, N.A. Popov, S.N. |
| author_sort |
Dolbin, A.V. |
| title |
Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects |
| title_short |
Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects |
| title_full |
Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects |
| title_fullStr |
Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects |
| title_full_unstemmed |
Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects |
| title_sort |
kinetics of ⁴he gas sorption by fullerite c₆₀. quantum effects |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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2010 |
| topic_facet |
Наноструктуры при низких температурах |
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http://dspace.nbuv.gov.ua/handle/123456789/117541 |
| citation_txt |
Kinetics of ⁴He gas sorption by fullerite C₆₀. Quantum effects / A.V. Dolbin, V.B. Esel'son, V.G. Gavrilko, V.G. Manzhelii, N.A.Vinnikov, S.N. Popov // Физика низких температур. — 2010. — Т. 36, № 12. — С. 1352–1355. — Бібліогр.: 16 назв. — англ. |
| series |
Физика низких температур |
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2025-07-08T12:26:19Z |
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| fulltext |
© A.V. Dolbin, V.B. Esel'son, V.G. Gavrilko, V.G. Manzhelii, N.A.Vinnikov, and S.N. Popov, 2010
Fizika Nizkikh Temperatur, 2010, v. 36, No. 12, p. 1352–1355
Kinetics of 4He gas sorption by fullerite C60.
Quantum effects
A.V. Dolbin, V.B. Esel'son, V.G. Gavrilko, V.G. Manzhelii, N.A.Vinnikov, and S.N. Popov
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
Received August 2, 2010
The kinetics of helium gas sorption by a C60 powder and subsequent desorption of the 4He impurity from the
saturated powder has been investigated in the temperature interval 2–292 K. Evidence is obtained that supports
the existence of two stages in the temperature dependences of sorption and desorption. The stages account for
the different times taken by helium to occupy the octahedral and tetrahedral interstices in the C60 lattice. The
characteristic times of sorption and desorption coincide. It is found that the temperature dependences of the cha-
racteristic times of occupying the octahedral and tetrahedral interstices are nonmonotonic. As the temperature is
lowered from 292 to 79.3 K, the characteristic times increase, which indicates a predominance of thermally acti-
vated diffusion of helium in C60. On a further decrease to T = 10 K the characteristic times reduce over an order
of magnitude. Below 8 K the characteristic times of sorption and desorption are temperature-independent. This
suggests a tunnel character of 4He diffusion in C60.
PACS: 68.43.Mn Adsorption kinetics.
Keywords: sorption kinetics, C60, 4He.
1. Introduction
Since the discovery of fullerenes in 1985 [1], carbon
nanomaterials have been attracting continuous attention.
Among the fullerenes known, C60 has been investigated
most intensively. C60 molecules form a molecular crystal
— fullerite which has a fcc lattice above 260 K. In the ful-
lerite crystal C60 molecules are orientationally disordered
and perform a weakly hindered rotation. At temperature T
~ 260 K C60 undergoes a phase transition to a partly orien-
tationally-ordered phase having a simple cubic lattice. On a
further decrease in the temperature the orientations of the
molecules grow quenched at T ~ 90 K and an orientational
glass is formed in which the C60 molecules have no long-
range orientation order. The crystal lattice of C60 has large
enough interstitial voids which can be occupied by rela-
tively small molecules of other substances. There are one
octahedral and two tetrahedral voids per molecule within
the C60 lattice.
Occupation of these voids by impurities can lead to the
formation of systems with qualitatively new properties.
Such changes are particularly pronounced at low tempera-
tures at which quantum effects appear. In particular, when
the interstitial cavities of a crystal C60 lattice are filled with
atoms of alkali metals, such a solution can change into the
superconducting state at temperatures below 33 K [2]. The
occupation of a C60 lattice by gas atoms and molecules
provokes phase transformations between different orienta-
tional glasses of C60 near the boiling temperature of liquid
helium [3–9].
Quantum effects can be caused by the tunnel motion of
the impurity atoms or molecules in C60. The probability of
the tunnel motion of impurities increases as the impurity
— C60 lattice interaction and the mass and size of the im-
purity atom/molecule decrease. 4He–C60 solutions there-
fore seem to be most promising for detecting the tunnel
motion of impurity molecules. The kinetics of sorption and
desorption is essentially dependent on the impurity diffu-
sion and must be sensitive to the mechanism of impurity
(He atoms) travel in solid C60 .
To our knowledge, the kinetics of helium sorption in
fullerite C60 has been investigated by two research groups.
The investigation of the effect of He atom intercalation
upon the lattice parameter of C60 by the x-ray diffraction
method [10,11] shows that the saturation of C60 with 4He
proceeds in two stages. According to the authors’ conclu-
sion, the impurity fills first the octahedral and then the te-
trahedral subsystems of voids in the C60 crystal. Note that
the latter subsystem is filled about an order of magnitude
slower than the octahedral one. The kinetics of 4He and
3He sorption in a 80% C60–20% C70 fullerite mixture was
Kinetics of 4He gas sorption by fullerite C60. Quantum effects
Fizika Nizkikh Temperatur, 2010, v. 36, No. 12, p. 1353
investigated at 77 and 300 K [12]. The authors [12] de-
scribed the time dependence of sorption with a single ex-
ponent and observed a slight decrease in the sorption time
as the temperature changed from 300 to 77 K.
In this study the temperature dependence of the kinetics
of sorption and subsequent desorption of 4He from a C60
powder was investigated in the temperature interval 2–
292 K using the technique of measuring the time depen-
dence of the pressure of the 4He gas that was in contact
with the C60 powder within a closed volume.
2. Experimental technique
The kinetics of 4He sorption and desorption in the 4He–
C60 system was investigated on a laboratory bench, its de-
sign and operation being detailed elsewhere [13]. The used
C60 powder of mass 515.2 mg had grains about 1 μm in
size. Its purity was 99.99 wt.%. To remove possible gas
impurities and moisture, the powder was evacuated before
measurement for 72 hours at T ~ 450 oC. Then during a
short time (~30 min in the air atmosphere) the powder was
transferred to the measuring cell and evacuated again at
room temperature for 48 h.
The kinetics of 4He sorption and desorption was in-
vestigated at 292 K, then at T = 79.3 K and in the interval
2–10 K. At T = 292 K and T = 79.3 K C60 was saturated
under the 4He pressure of 760 Torr. In the interval 2–10 K
the pressures of the 4He gas were 2 and 10 Torr. Since at
T = 2–10 K the pressure of the He gas in the measuring cell
was much lower than the saturated vapor pressure of he-
lium (23.8 Torr at T = 2 K [14]), this prevented condensa-
tion of the 4He vapor and the formation of 4He films on the
surface of the powder grains and the cell walls.
The pressure variations in the closed volume of the
measuring cell were measured continuously during satura-
tion using a capacitive pressure transducer (MKS «Bara-
tron») permitting us to measure low pressures with the
error 1·10–3 Torr. On reaching the equilibrium pressure,
the 4He gas was removed fast (~1 min) from the measuring
cell and the cell was sealed again. The pressure variations
were measured in the process of 4He desorption from the
powder. When the investigation of desorption was com-
pleted and the pressure in the cell with the powder became
equilibrium, the 4He impurity that might still remain in the
powder was removed through evacuation at room tempera-
ture. The pressure control in the measuring cell after evac-
uation showed a practically total absence of 4He desorption
from the powder in the vacuum 10–3 Torr. After removing
helium, the powder was cooled down to the subsequent
temperature of measurement and the process of saturation
was repeated. The data acquisition system of the laboratory
bench allowed recording the gas pressure at an interval of
0.2 s and thus enabled a reliable registration of high-speed
pressure variations in the measuring cell.
3. Results and discussion
In this study we have obtained evidence that supports
the previous results [10,11] on a two-stage process of satu-
ration of C60 with the 4He impurity. The experimental de-
pendence of pressure variations in the course of He sorp-
tion or desorption (see Fig. 1) was approximated by a sum
of two exponential functions having different characteristic
times (τ1, τ2).
1 2[(1 exp ( / )) (1 exp ( / ))]P A t t C= − − τ + − − τ + . (1)
The parameters τ1, τ2, A, and C were obtained by fitting
Eq. (1) to the experimental results.
The conclusions of Refs. 10, 11 suggest that the expo-
nents τ1 and τ2 correspond to the characteristic times dur-
ing which the He atoms can occupy the octahedral and
tetrahedral subsystems of the interstitial sites in the C60
lattice. The characteristic times of occupying the octahe-
dral interstices τ1 are one or two orders of magnitude
shorter than the characteristic times taken to occupy the
considerably smaller tetrahedral voids τ2.
Fig. 1. Experimental curves of pressure variations in the course of
4He desorption from a C60 powder at different T.
1,5
20 40 60 80 1000
0,5
1,0
1,5
2,0
T = 10 K
T = 292 K
t, h
T = 79.3 K
P
,
to
rr
P
,
to
rr
0 1 2 3 4
0,5
1,0
T = 10 K
t, h
A.V. Dolbin, V.B. Esel'son, V.G. Gavrilko, V.G. Manzhelii, N.A.Vinnikov, and S.N. Popov
1354 Fizika Nizkikh Temperatur, 2010, v. 36, No. 12
Note that the time dependences of pressure variations
measured on 4He sorption and desorption at the same val-
ues of the powder temperature are qualitatively similar and
their characteristic times coincide within the accuracy of
the measuring technique. Besides, in the temperature inter-
val 2–10 K the characteristic times τ1 and τ2 were inde-
pendent of the starting pressure of the 4He gas in the mea-
suring cell. The temperature dependences of the
characteristic times of 4He sorption by C60 powder and the
proper times of 4He gas thermalization in the measuring
system are illustrated in Fig. 2. The thermalization times
were estimated in the absence of C60 powder in the mea-
suring cell. The characteristic times τ1 and τ2 exceed the
proper times of 4He thermalization at least by an order of
magnitude in the whole interval of the measurement tem-
peratures. Thus, the proper times of 4He gas thermalization
in the measuring cell have practically no effect on the tem-
perature dependences τ1(T) and τ2(T).
As the temperature is lowered from 292 to 79.3 K, the
characteristic times of 4He sorption by C60 increase, which
corresponds to the thermally activated mechanism of diffu-
sion. However, on a further drop of the powder tempera-
ture (to 10 K and lower) the characteristic times of sorption
decrease sharply. Besides, below 8 K the characteristic
times are temperature independent. This leads us to assume
that below T = 10 K tunneling of 4He atoms becomes a
dominant process in fullerite which determines the rate of
4He sorption (desorption) in C60 .
It should be noted that the quantity of helium sorbed by
the C60 powder at 2 K ≤ T ≤ 10 K under the 4He gas pres-
sure 10 Torr does not exceed 2 mol.%. This agrees with the
conclusions of experimental investigations in which the
limiting solubility of helium in fullerite in the temperature
interval 1.50–1.68 K was no more than 5% [15,16]. On the
other hand, our estimates of the 4He concentration are over
an order of magnitude higher than the amount of helium
that could be sorbed at the grain boundaries in C60 poly-
crystals with a grain size of ~1 μm.
4. Conclusions
The performed investigations of the kinetics of 4He
sorption by a C60 powder and the subsequent 4He desorp-
tion from the saturated powder show that the characteristic
times of occupation of the octahedral and tetrahedral in-
terstitial voids in the C60 lattice exhibit a nonmonotonic
dependence on temperature. As the temperature of the
sample lowers from room temperature to 79.3 K, the cha-
racteristic times of 4He sorption by C60 increase, which
corresponds to thermally activated 4He diffusion in C60.
A further decrease in the temperature of the C60 powder
causes a sharp reduction of the characteristic times in the
interval 2–10 K. Besides, at 2 K ≤ T ≤ 8 K the characteris-
tic times are independent of temperature. This suggests that
below 10 K tunneling of He atoms becomes dominant in
C60 and determines the rate of 4He sorption.
The authors are indebted to Prof. L.A. Pastur for fruitful
discussions.
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Fig. 2. The temperature dependence of the characteristic times of
4He sorption by fullerite C60 (circles — τ2, squares — τ1, × —
proper times of 4He thermalization in the measuring system).
1 10 100
10–1
100
101
102
103
104
105
T, K
�2
�1
�
,
s
Kinetics of 4He gas sorption by fullerite C60. Quantum effects
Fizika Nizkikh Temperatur, 2010, v. 36, No. 12, p. 1355
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