Nano-sized Cu6Sn5 alloy prepared by a co-precipitation reductive route

Article abstract of DOI:10.1016/j.poly.2010.02.035

Nano-sized Cu₆Sn₅ alloy powders were prepared by a co-precipitation reductive route using a hydrothermal method at 80 °C. The nano-size and morphology of the synthesized Cu₆Sn₅ alloy powders were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained morphologies, chemical compositions are comparatively discussed. A variety of synthesis parameters, such as time, capping agent and sort of reductant, has an effect on the morphology of the obtained materials, and will be particularly highlighted.

Full text of DOI:10.1016/j.poly.2010.02.035

Polyhedron 29 (2010) 1796–1800
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Polyhedron
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Nano-sized Cu6Sn5 alloy prepared by a co-precipitation reductive route
b
a
Masoud Salavati-Niasari a,b, , Mehdi Bazarganipour , Fatemeh Davar
*
a Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran
b Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Nano-sized Cu6Sn5 alloy powders were prepared by a co-precipitation reductive route using a hydrother-
mal method at 80 °C. The nano-size and morphology of the synthesized Cu6Sn5 alloy powders were eval-
uated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). The obtained morphologies, chemical compositions are comparatively discussed. A
variety of synthesis parameters, such as time, capping agent and sort of reductant, has an effect on the
morphology of the obtained materials, and will be particularly highlighted.
Received 26 October 2009
Accepted 17 February 2010
Available online 6 March 2010
Keywords:
Co-precipitation
Reductive
Ó 2010 Elsevier Ltd. All rights reserved.
Hydrothermal
Nano-sized alloy
1. Introduction
but a low reversible capacity. It has been reported that the
cycling performance of tin could be significantly improved by
Recently much effort has been applied to the synthesis of uni-
formly sized and shape-controlled particles of metal oxide, sulfides
or alloys [1–6]. Nano-sized metallic alloys have shown novel opti-
cal, catalytic, electrical and magnetic properties with respect to
those of the pure metals and corresponding bulk materials. In re-
cent years, many authors [7–9] have been working upon alterna-
tive anode materials for secondary lithium batteries. Different
metals (Al, Pb and Sn) and intermetallic compounds such as
Cu6Sn5, Sn–SnSb, Ni–Sn, SnAg and Sn2Fe–C have been investigated
as potential perspective anode materials, and some of them pos-
sess higher specific capacity than those of graphite and other car-
bon materials that are presently used.
addition of a secondary component to form intermetallic com-
pounds such as Sn2Fe [11], Sn2FeC [12], Cu6Sn5 [13,14] and
NixSn [15].
Several methods, such as high-energy ball-milling [16–19],
vapor deposition [20], electro deposition [21–23] and reductive
co-precipitation [24–29], have been tried to prepare nano-sized
alloys with different morphologies. Baskoutas et al. have success-
fully prepared different nano-sized alloys such as supersaturated
Ag–Cu [30], Zr55Cu19Ni8Al8Si5Ti5 [31], Zr-based alloys [32] and
others [33] by the high-energy ball-milling method. Recently
our group has synthesized a Bi2Te3 nano-structure with different
morphologies by a hydrothermal process based on the reaction
between Bi(NO3)3, TeCl4, and KBH4 in water under various con-
ditions [34].
Among the above-mentioned methods for preparing nano-
sized alloys, reductive co-precipitation is shown as a simple
and easy way to obtain good morphology. In continuation of
the development of simple synthesized nano-sized alloys, we
have investigated the influence of capping agent, stoichiometric
ratio, sort of reductant and time on the morphology of nano-
sized alloy materials prepared by reductive co-precipitation.
The Cu6Sn5 alloy was chosen as the material to be investigated
as it has several advantages, including a strong structural rela-
tionship existing between the parent binary intermetallic elec-
trode and its lithiated product [35–37], relatively inexpensive
elements and environmental friendliness [38–40]. To the best
of our knowledge, this is the first report on the synthesis of
nano-sized Cu6Sn5 alloy via the co-precipitation method with
different capping agents.
However, the problems with volume changes resulting from
phase transitions have not yet been solved. In 1999, Kepler et al.
discovered that lithium could be intercalated into the Cu6Sn5 alloy,
forming the system LixCu6Sn5 [1]. Thus, this is a material with a
theoretical gravity capacity of about 350 mA h gÀ1, and with signif-
icantly higher volume capacity, corresponding to 1656 mA h mlÀ1
in comparison with commercial LiC6 [1].
,
Many studies have been focused on lithium storage alloys
since the Fuji photo film company issued a patent on tin-based
amorphous composite oxides (TCO) as novel anode materials for
lithium-ion batteries in 1996 [10]. Compared with the carbona-
ceous materials, lithium storage alloys showed a large capacity,
* Corresponding author. Address: Institute of Nano Science and Nano Technology,
University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran. Tel.:
+98 361 5555333; fax: +98 361 5552930.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.02.035

M. Salavati-Niasari et al. / Polyhedron 29 (2010) 1796–1800
1797
2. Experimental
3. Results and discussion
2.1. Materials and physical measurements
The composition of the as-prepared product was determined
by XRD (Fig. 1). All peaks in the patterns correspond to the
reflections of monoclinic phase Cu6Sn5, with cell constants
a = 11.033 Å, b = 7.29 Å, c = 9.83 Å, which are in agreement with
JCPDS 45–1488. The average particle size of the sample is about
37 nm, estimated through the Scherrer formula (Fig. 1a). In com-
parison with Cu6Sn5, prepared in the presence of pn as a capping
agent, Cu6Sn5 prepared in the presence of PEG 600 and PEG
20000 as capping agents, showed an increase in the broadening
of a peak at half-height, as the result of the decrease in particle
size to 29 and 25 nm (Fig. 1b and c). On the other hand, with a
change in the Cu:Sn stoichiometric ratio, Cu6Sn4 was synthesized
(Fig. 2).
All the chemicals reagents used in our experiments were of ana-
lytical grade, were purchased from Merck and were used as re-
ceived without further purification. XRD patterns were recorded
by a Rigaku D-max C III, X-ray diffractometer using Ni-filtered Cu
Ka radiation. Scanning electron microscopy (SEM) images were ob-
tained on a Philips XL-30ESEM equipped with an energy dispersive
X-ray spectroscope. Transmission electron microscopy (TEM)
images were obtained on a Philips EM208 transmission electron
microscope with an accelerating voltage of 100 kV.
2.2. Synthesis of nano-sized Cu6Sn5 alloy
The morphology of the product was examined by SEM. Fig. 3a
and b contains the SEM pictures of samples of nano-sized alloy.
From the micrograph, it is observed that the nano-sized alloy is
agglomerated. To reach an ideal morphology, we prepared nano-
sized Cu6Sn5 alloy with various capping agents, such as PEG 600
and PEG 20000, in the presence of KBH4 as a reductant (Fig. 3c
and d). It shows that the utilization of PEG 20000 declines the
agglomeration of the nano-sized alloy and the growth of the
particles.
In continuation, the effect of the reductant sort on the morphol-
ogy of nano-size alloy in the presence of PEG 20000 as a capping
agent was investigated. Fig. 4 shows that the reducing agents do af-
fect the morphology of the nano-sized alloy. The two other reduc-
ing agents that were applied are N2H4 and Zn.
Nano-sized Cu6Sn5 alloy was prepared by the co-precipitation
reductive method. CuCl2 and SnCl2 were used as the precursors in
the hydrothermal synthesis. The precursors, with a Cu:Sn stoichi-
ometric ratio of 1.2:1, were put into a Teflon-lined autoclave. The
autoclave was then filled with water up to 80% of its volume.
After adding sufficient KBH4 as the reductant and pn (propylene
diamine) as a complexing agent, the autoclave was sealed imme-
diately and heated to 80 °C for the synthesis reaction. After 5 h,
the autoclave was cooled down to room temperature naturally.
The obtained precipitates were separated by centrifugation,
washed with deionized water followed by ethanol for three times,
and dried at 100 °C under vacuum for 24 h. For nano-sized Cu6Sn4
alloy, the experimental method was similar except a Cu:Sn stoi-
chiometric ratio of 1.5:1 was used. The structure and morphology
of the Cu6Sn5 and Cu6Sn4 powders were characterized by XRD
and TEM.
The advantage of the wet preparation method is that the re-
duced metal cations are homogeneously dissolved in solution.
Whereas the reduction with KBH4 and N2H4 proceeded in a
Fig. 1. XRD pattern of Cu6Sn5, prepared at 80 °C for 5 h: (a) pn, (b) PEG 600 and (c) PEG 20000 as the capping agent and KBH4 as the reductant.

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M. Salavati-Niasari et al. / Polyhedron 29 (2010) 1796–1800
Fig. 2. XRD pattern of Cu6Sn4, prepared at 80 °C for 5 h, pn as the capping agent and KBH4 as the reductant.
Fig. 3. SEM picture of (a) Cu6Sn5 and pn as the capping agent (b) Cu6Sn4 and pn as the capping agent (c) Cu6Sn5 and PEG 600 as the capping agent (d) Cu6Sn5 and PEG 20000 as
the capping agent, prepared at 80 °C for 5 h with KBH4 as the reductant.
homogeneous way, the metal cation solution and the reductant
solution being liquids, the reduction of the liquid metal cation
solution with solid Zn powder is a heterogeneous process and
as such is limited by the interface area of the Zn surface in con-
tact with the solution. The consequences may be dramatic. The
strong reductants KBH4 and N2H4, in combination with stirring
rapidly, created a large number of nuclei and further growth
of the nuclei was limited. As a result, many small particles were
obtained. The reduction in the presence of Zn proceeds only
two-dimensionally, i.e., at the interface of the Zn powder with
the metal cation solution. The rate of reduction is further lim-
ited by the mass transport of the metal cation solution to the
Zn surface. Therefore, depletion of metal cations near the inter-
face might occur. As a consequence of the rate and surface area
limitation, crystal growth is favored over nuclei formation, with
the result of larger particles [41].
The reduction with Zn generally yields materials with larger
particle sizes. This may be explained by the facts that the standard
reduction potential of Zn is higher than that of KBH4 (À0.763 V ver-
sus À1.24 V) and that reduction with Zn is a heterogeneous pro-
cess, with the reduction being limited to the interface between
the solid Zn and the cation solution, whereas the reduction with
KBH4 takes place in homogenous solution. Hence, the reduction
with Zn is expected to be milder and slower, and crystal growth

M. Salavati-Niasari et al. / Polyhedron 29 (2010) 1796–1800
1799
Fig. 4. SEM picture of Cu6Sn5 in presence of (a) N2H4 and (b) Zn as the reductant, prepared at 80 °C for 5 h with PEG 20000 as the capping agent.
Fig. 5. SEM picture of Cu6Sn5 in presence of (a) N2H4 and (b) Zn as the reductant prepared at 80 °C for 12 h with PEG 20000 as the capping agent.
rate in comparison with nucleation is favored, so larger particles
are yielded [42].
With the strong reducing power of KBH4, gaseous by-products,
such as H2, CuHx and SnHx, are formed beside the multiphase
Cu6Sn5 phase. The related strong gas evolution adjacent to the
nucleus formation site may hinder the growth of large particles
and or agglomerates. Zn is a less strong reducing agent, so that
in aqueous solution H2 is only a minor by-product.
Fig. 5 reveals the time effect on the morphology of the nano-
sized alloy. On increasing the time from 5 to 12 h, the nano-sized
alloy showed a dense agglomerate and the particle size was in-
creased (Fig. 5a and b).
The morphology and size distribution of the products were
further studied by TEM. A TEM photograph of the product is gi-
ven in Fig. 6. The sizes of nano-sized alloy obtained from the
TEM studies are in close agreement with the XRD diffraction pat-
terns, which show sizes of 35–41 nm (Fig. 6). The TEM image
(Fig. 6) shows the presence of dense agglomerates. The particles
have an irregular shape and their distribution is not uniform
(35–41 nm).
In comparison to other similar work, illustrated in Table 1,
our work has various benefits, such as the Cu6Sn5 nano-sized al-
loy prepared in this work has high purity and crystallinity with
only Cu6Sn5 being found, without any other intermetallic com-
pounds e.g. Cu3Sn or metal oxides. Also the particle size is
smaller than most other works and for the first time, we have
used different reductive agents to prepare the Cu6Sn5 nano-size
alloy.
Fig. 6. TEM picture of Cu6Sn5 prepared at 80 °C for 5 h, pn as the capping agent and
KBH4 as the reductant.

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M. Salavati-Niasari et al. / Polyhedron 29 (2010) 1796–1800
Table 1
Characterization comparison of Cu6Sn5 nano-sized alloys from other similar works.
Particle size
Morphology
Method
Ref.
45 nm
dendrite
amorphous
particle
mixture Cu6Sn5, Cu3Sn and Cu2O
mixture
spherical
solution route
reverse microemulsion
chemical method
reductive precipitation
borohydride reduction
spray pyrolysis
[43]
[44]
[45]
[46]
[47]
[48]
50–60 nm
30–40 nm
11–23 nm
1.5–0.7
lm
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4. Conclusion
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This approach to nano-sized Cu6Sn5 alloy is simple, convenient
and effective, and holds potential for large-scale syntheses needed
for commercial applications. Most important of all, this new ap-
proach can yield a high purity for Cu6Sn5, without any other inter-
metallic compounds or metal oxides, by a simple and low cost
hydrothermal method.
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Authors are grateful to the council of Iran National Science
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