Synthesis of Bi2Sr2CaCu2Oy nanowire and its superconductivity

Article abstract of DOI:10.1016/j.ssc.2008.09.012

The superconducting Bi₂Sr₂CaCu₂O_y nanowires were synthesized by a sol-gel template route in a porous anodic aluminum oxide (AAO) membrane. Field emission scanning electron microscopy (FESEM) confirmed that the monodisperse cylindrical pores of alumina membrane were filled with superconducting nanowire arrays. The nanowires were essentially polycrystalline as determined by high resolution transmission electron microscope (HRTEM) images and selected electron diffraction (SAED) analysis. The onset transition temperature of the Bi₂Sr₂CaCu₂O_y nanowires is 84K, which is close to the transition temperature of bulk material. The superconducting hysteresis loop measurement indicates that the critical current density decreases with increasing applied magnetic field and temperature.

Full text of DOI:10.1016/j.ssc.2008.09.012

Solid State Communications 148 (2008) 452–454
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Solid State Communications
journal homepage: www.elsevier.com/locate/ssc
Synthesis of Bi2Sr2CaCu2Oy nanowire and its superconductivity
∗
S.H. Lai, Y.C. Hsu, M.D. Lan
Department of Physics, National Chung Hsing University, Taichung 402, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
The superconducting Bi2Sr2CaCu2Oy nanowires were synthesized by a sol–gel template route in
a porous anodic aluminum oxide (AAO) membrane. Field emission scanning electron microscopy
(FESEM) confirmed that the monodisperse cylindrical pores of alumina membrane were filled with
superconducting nanowire arrays. The nanowires were essentially polycrystalline as determined by high
resolution transmission electron microscope (HRTEM) images and selected electron diffraction (SAED)
analysis. The onset transition temperature of the Bi2Sr2CaCu2Oy nanowires is 84K, which is close to the
transition temperature of bulk material. The superconducting hysteresis loop measurement indicates
that the critical current density decreases with increasing applied magnetic field and temperature.
© 2008 Elsevier Ltd. All rights reserved.
Received 24 March 2008
Received in revised form
21 July 2008
Accepted 4 September 2008 by P. Chaddah
Available online 10 September 2008
PACS:
74.72.Hs
74.48.Na
81.07.-b
81.20.Fw
Keywords:
A. Nanowires
A. Superconductors
B. Sol–gel
B. Anodic aluminum oxide
1. Introduction
sheet (99.99%) was electropolished in H3PO4 solution to achieve
a smooth surface. After rinsed with ethanol and distilled water,
Since carbon nanotubes were discovered in 1991 [1], drastic
interest in space-restrained superconductivity has aroused volu-
minous research of the worldwide nanotechnology [2–8]. Fabrica-
tion and investigations of the nanoscale devices of cuprates not
only provide the fundamental understanding of the effect of di-
mensionality and size on their superconductivity but also help to
figure out the restriction of the practical application of supercon-
ducting nanoscale devices. There have been only a few reports on
the synthesis of cuprates nanostructure. Y.F. Zhang et al. synthe-
sized YBCO nanorods by laser ablation [9]. Xu. Jian et al. fabricated
YBCO nanowires from a template-directed sol–gel route [10]. Un-
fortunately, the superconductivity of these nanostructures weren’t
further discussed. In the present work, we extended the synthe-
sized nanowires to Bi-2212 superconducting cuprates via a sol–gel
template method and confirmed its superconductivity as well.
the sample was mounted to serve as anode for anodization. The
anodizing process was carried out under constant voltage of 50 V
◦
in 0.4 M oxalic acid electrolyte at 2 C for 3 h. The AAO membrane
was detached from the Al substrate in a saturated CuCl2 solution.
The membrane was rinsed with distilled water and then immersed
◦
in 5% H3PO4 solution at 30 C for 30 min in order to widen the pores
and dissolve the barrier layer.
2.2. Sol–gel process and fabrication of Bi2Sr2CaCu2Oy nanowires
A nominal stoichiometry of Bi2Sr2CaCu2Oy was chosen for the
preparation of the precursors by sol–gel routes. High purity Bi2O3,
Sr(NO3)2,CaO, CuO powders were used as the starting materials in
synthesizing process. The molar ratio of Bi3+:Sr2+:Ca2+:Cu2+
=
◦
2:2:1:2 of above materials were dissolved at 70 C in distilled water
containing ethylenediamine tetraacetic acid (EDTA) as chelant
agent. The pH of this mixture solution was adjusted to 7–8 by
using ammonia. Furthermore, the mixture was hydrolyzed to form
2. Experimental
2.1. Preparation of anodic aluminum oxide (AAO) template
◦
a dispersed blue colloidal solution at 70 C under continuous
stirring for 8 h. Then a piece of AAO membrane was dipped into
this transparent hot sol under ultrasonic treatment, and kept at
Porous AAO membrane was prepared by Al plate anodizing
process [11,12]. After degreasing in acetone, the high purity Al
◦
70 C for 12 h. The sol containing AAO membrane was gelled to
◦
shards by slow evaporation at 70 C. To form the superconducting
∗
phase, the obtained gel/AAO composite was further heated to
Corresponding author. Tel.: +886 4 22840427x396; fax: +886 4 22862534.
E-mail address: lan@phys.nchu.edu.tw (M.D. Lan).
◦ ◦
875 C at heating rate of 60 C an hour, held for 2 h in air, and
0038-1098/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2008.09.012

S.H. Lai et al. / Solid State Communications 148 (2008) 452–454
453
Fig. 2. EDX spectrum of Bi2Sr2CaCu2Oy nanowires fabricated in pores of AAO
membrane.
Fig. 1. (a) Cross-sectional view of empty AAO membrane. (b) Cross-sectional view
of of the Bi2Sr2CaCu2Oy nanowires/AAO composites.
Fig. 3. TEM image of the Bi2Sr2CaCu2Oy nanowires. The inset is the corresponding
SAED pattern.
then the specimen was cooled to ambient temperature. Finally, the
AAO membrane incorporated with Bi2Sr2CaCu2Oy nanowires was
picked out, and then carefully rubbed away redundant powders
covering both faces of the membrane.
template-directed sol–gel synthesis, the Bi2Sr2CaCu2Oy nanowires
encapsulated in empty pores of AAO membrane could be easily
observed from FESEM image of the cross-sectional view of
Bi2Sr2CaCu2Oy nanowires/AAO composites (Fig. 1b).
The EDX spectrum of Bi2Sr2CaCu2Oy nanowires fabricated in
pores of AAO membrane was carried out for qualitative analysis
of the nanowires/AAO composites (Fig. 2). The characteristic
peaks indicate that elements Bismuth, Calcium, Copper, Strontium,
Oxygen and Aluminum were detected. The peak Aluminum comes
from the AAO membrane used to be the template in nanowire
fabricating process.
Further information about the microstructure of Bi2Sr2CaCu2Oy
nanowires can be obtained by the TEM/HRTEM measurement.
As prepared for the TEM measurement, we simply ground the
membrane into menthol rather than dissolving them in alkaline
solvent base in order to avoid introducing impurities in the
measurement. Fig. 3 shows the TEM image of Bi2Sr2CaCu2Oy
nanowires, the nanowires are nearly 40 nm in diameter. The
size is not as large as the pores of AAO membrane due to the
dehydration of heating process. The inset in figure is the SAED
pattern of Bi2Sr2CaCu2Oy nanowire, in which six diffraction rings
correspond to the (220), (113), (024), (115), (135) and (117)
planes for polycrystalline Bi2Sr2CaCu2Oy with an orthorhombic
structure. The diffraction rings consist of rather sharp spots in
the SAED pattern surely indicate that the nanowires are well
crystallized. Fig. 4 is the HRTEM image of Bi2Sr2CaCu2Oy nanowire.
The image shows several lattice fringes that provides evidence of
the polycrystalline character.
2.3. Characterization
The morphology of Bi2Sr2CaCu2Oy nanowires embedded in AAO
membrane was investigated by FESEM (JOEL JSM-6700F, Japan).
The AAO membrane containing Bi2Sr2CaCu2Oy nanowires was
ground and dispersed into ethanol followed by ultrasonic treat-
ment for 20 min. Afterward, one drop of resulted suspension was
placed on a carbon coated copper grid and then dried at room
temperature for TEM (JOEL JEM-2010, Japan) visualization. The se-
lected electron diffraction (SAED) and the energy dispersion spec-
troscopy (EDX) analysis were performed to identify the lattice
structure as well as the composition. Dc magnetization measure-
ment was carried out by a superconducting quantum interference
device (SQUID) magnetometer (Quantum Design, USA).
3. Results and discussion
In order to understand the crystallization of Bi2Sr2CaCu2Oy
synthesized in AAO and avoid yielding undesired template
Al2O3 nanowires, we observed the Bi2Sr2CaCu2Oy nanowires/AAO
composites by FESEM directly. The diameter of as-prepared AAO
template with array of cylindrical pores was 100 nm, the cross-
sectional view of the AAO template characterized by FESEM
investigation also shows the straight cylindrical pores of AAO
template and up to several µm in length (Fig. 1a). After the

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S.H. Lai et al. / Solid State Communications 148 (2008) 452–454
Fig. 6. Hysteresis loop of the Bi2Sr2CaCu2Oy nanowires fabricated in pores of AAO
membrane.
Fig. 4. HRTEM image of the Bi2Sr2CaCu2Oy nanowires.
4. Conclusion
In summary, superconducting Bi2Sr2CaCu2Oy nanowires were
synthesized by a sol–gel template route in a porous anodic
aluminum oxide membrane. The SAED pattern verifies the
polycrystalline orthorhombic structure of the Bi2Sr2CaCu2Oy
nanowire. The low dc field magnetic response measurement shows
the onset transition temperature of the Bi2Sr2CaCu2Oy nanowires
is 84 K. The hysteresis loop measurement reveals that the critical
current density decreases with the increasing magnetic field and
temperature.
Acknowledgements
The authors would like to thank the National Science Council of
the Republic of China for financially supporting this research under
Contract No. NSC 95-2112-M-005-010-MY3.
Fig. 5. Superconducting shield curve of the Bi2Sr2CaCu2Oy nanowires fabricated in
pores of AAO membrane. The data was measured under ZFC at 10 Oe.
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Fig. 5 shows the zero-field-cooled (ZFC) low magnetic field
response of Bi2Sr2CaCu2Oy nanowires/AAO composites in the
temperature range of 5 K to 100 K. According to this shielding
curve, the onset temperature of inductive superconducting
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