World Journal Of Engineering
ATOMIC MOBILITY, FREEZING, AND SUPERCONDUCTIVITY IN
ARRAYS OF METALLIC PARTICLES WITHIN NANOPOROUS
MATRICES
E.V. Charnaya 1,2, Cheng Tien 1,3, M.K. Lee 1, D. Y. Xing 4, B.F. Borisov 2, and Yu. A. Kumzerov 5
1
Department of Physics, National Cheng Kung University, Tainan, 701 Taiwan
Institute of Physics, St Petersburg State University, St Petersburg 198904, Russia
3
Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 701, Taiwan
4
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University,
Nanjing 210093, People's Republic of China
5
A. F. Ioffe Physico-Technical Institute RAS, St Petersburg 194021, Russia
2
Introduction
Results and discussion
At present, composites with nano-size metallic
inclusions attract the increased attention because of
their various perspective technological applications.
Properties of confined metallic nanoparticles are
influenced by size-effects and, additionally, by
interparticle coupling and interaction with the matrix.
Therefore, nanocomposites with small metallic
particles bear features which can differ remarkably
from those in relevant bulk materials and nanoparticles.
In the present report we focus the attention onto
nanocomposites consisted of opal and porous glass
matrices which pores are filled with gallium, indium,
lead, tin, bismuth, and their alloys [1-8]. The atomic
mobility in confined melts, melting and freezing in
metallic particles within pores, and superconductivity
in the nanocomposites will be discussed.
Atomic diffusion in confined melts was found to slow
down drastically compared to the bulk counterparts
[2,5,8]. The correlation time of atomic mobility was
found to depend on the pore size and increase more
than by an order of magnitude for fine pores.
Additional slowing down in atomic mobility was
observed for the confined metals in the supercooled
state. The increase of the correlation time of atomic
mobility was revealed from the experimentally
observed drastic acceleration of the quadrupole
contribution to nuclear spin relaxation under
nanoconfinement. The decrease in the relaxation time
due to such an effect is illustrated in Table 1 for the
Ga-In eutectic embedded into a porous glass with 5 nm
pores [2].
Table 1. Spin relaxation time in bulk and confined
Ga-In eutectic
Experimental
The pore sizes in the opal and porous glass matrices
which were used to fabricate the nanocomposites were
in the range from 2 to 200 nm. The liquid metals and
alloys were embedded into pores in liquid state under
high pressure.
Slowing down of atomic diffusion and changes in
electron susceptibility were studied by NMR using
Bruker pulse spectrometers. Melting and freezing in
confined metallic particles were studied by NMR and
acoustic techniques. Superconductivity in the
nanocomposites was studies using Quantum Design
PPMS and SQUID magnetometer. X-ray powder
diffraction was used to reveal the structure of metals
under confinement.
isotope
alloy
T1 (s)
71
bulk
522
Ga
confined
54
115
bulk
222
In
confined
7.5
The Knight shift of the NMR lines which is
proportional to the electron susceptibility was shown to
decrease in liquid confined metals and alloys compared
to the bulk melts. The reduction of the Knight shift
enhanced with decreasing the pore size [7].
The melting and crystallization phase transitions
for metallic components of nanocomposites were
noticeably moved to lower temperatures and strongly
diffused. For some metals as mercury and tin the
occurrence of the liquid skin upon melting was
suggested [6]. The pronounced hysteresis between
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World Journal Of Engineering
M'' (emu/cm3)
melting and freezing was ascribed to heterogeneous
nucleation under confinement.
The step-like freezing and melting of gallium
within pores was found to occur due to the emergence
of different crystalline phases. The particular phases
which can form within pores depended on pore size
and geometry. Three new phases were seen for gallium
within porous glasses and opal matrices, -Ga, -Ga [3],
and -Ga [4]. The melting and crystallization processes
within a porous glass with 7 nm pores are shown in
Fig.1.
Intensity (rel. units)
0.006
2
4
6
8
T (K)
Fig.2. Temperature dependences of the imaginary M
part of ac magnetization at external static
magnetic fields shown on the panel observed for
the lead-porous glass nanocomposite.
0.8
-Ga
Conclusions
0
1.2
Atomic mobility, electronic properties, melting and
freezing
phase
transitions,
structure,
and
superconductivity were studied in the arrays of metallic
and alloy particles embedded into nanoporous silica
matrices. The obtained results revealed new features
related to size effects and interparticle coupling.
0.8
-Ga
0.4
0
200
240
T (K)
280
Fig.1. Intensity of x-ray peaks for -Ga and -Ga
versus temperature for the gallium loaded
porous glass with pore size 7 nm. Open and
closed symbols correspond to cooling and
warming, respectively.
References
1. Y.S. Ciou, C. Tien, E.V. Charnaya, D.Y. Xing, Yu.A.
Kumzerov, M.K. Lee, and A.L. Pirozerskii. Double peaks on
ac magnetization in a superconducting Pb-porous glass
nanocomposite. Phys. Lett. A 374 (2010) 4942–4944.
2. E. V. Charnaya, C. Tien, M. K. Lee, and Yu. A.
Kumzerov. Atomic mobility in nanostructured liquid Ga-In
alloy. J. Phys.: Condens. Matter 22 (2010) 195108.
3. M. K. Lee, C. Tien, E. V. Charnaya, H.-S. Sheu, and Yu.
A. Kumzerov. Structural variations in nanosized confined
gallium. Phys. Lett. A 374 (2010) 1570–1573.
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Kumzerov. Superconductivity and structure of gallium under
nanoconfinement. J. Phys.: Condens. Matter 21 (2009)
455304.
5. E. V. Charnaya, C. Tien, M. K. Lee, and Yu. A.
Kumzerov. Slowdown of self-diffusion induced by partial
freezing in confined liquid indium. Phys. Rev. B 75 (2007)
212202.
6. E. V. Charnaya, C. Tien, M. K. Lee, and Yu. A.
Kumzerov. NMR studies of metallic tin confined within
porous matrices. Phys. Rev. B 75 (2007) 144101.
7. C. Tien, E. V. Charnaya, M. K. Lee, and Yu. A.
Kumzerov. Influence of pore size on the Knight shift in
liquid tin and mercury in a confined geometry. J.Phys.:
Condens. Matter 19 (2007) 106217.
8. E. V. Charnaya, T. Loeser, D. Michel, C. Tien, D. Yaskov,
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The superconducting transition temperatures for
newly observed gallium structures were much higher
than that for bulk -Ga. These findings are illustrated
in Table 2.
Table 2. Temperatures Tc of the superconducting
transition in confined gallium
crystalline
phase
Tc (K)
500 Oe
200 Oe
600 Oe
400 Oe
300 Oe
100 Oe
0
1.2
0.4
0.012
-Ga
-Ga
-Ga
7.1
6.7
6.3
Superconducting features of the nanocomposites
were shown to be generally similar to those of dirty
type-II superconductors. When the pore filling was
high enough, the whole nanocomposites were screened
from external magnetic field. A double step transition
was observed for nanocomposites when the filling was
incomplete. Phase transitions in vortex system were
also found. This is illustrated with double peaks in ac
magnetization for the Pb loaded porous glass (Fig.2)
[1]. For some nanocomposites we also observed
magnetic instabilities and fish-tail magnetization loops.
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