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Chemistry Letters Vol.34, No.1 (2005)
A Room Temperature Self-sacrificing Template Route to Ag Te Fibers
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ꢀ
Li Mu, Junxi Wan, Dekun Ma, Rui Zhang, Weichao Yu, and Yitai Qian
Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemistry,
Univeristy of Science and Technology of China, Hefei 230026, P. R. China
(Received October 25, 2004; CL-041254)
Tellurium fibers are first synthesized through the reduction
Synthesis of Ag2Te fibers: the freshly prepared Te fibers
(0.5 mmol) were added into a 20-mL aqueous solution contain-
ing 0.1 M AgNO3 in a conical flask. The solution was further
aged in the dark for 24 h at room temperature. Solid black sam-
ple was centrifuged, collected and dried at 50 C for 6 h under
ambient conditions.
of Na2TeO4 by hydrazine hydrate. The as-prepared tellurium fi-
bers are used as templates for further reaction with aqueous
AgNO3 solution to get Ag2Te fibers at room temperature.
ꢁ
X-ray powder diffraction (XRD) patterns were carried
out on a Philips X’ pert diffractometer with Cu Kꢀ radiation
Transition metal chalcogenides including sulfides, sele-
nides, and tellurides have attracted considerable attention in re-
cent decades due to their interesting properties and potential ap-
plications. Silver chalcogenides have been known as superionic
conductors. Among them, silver telluride exhibits some unique
properties, for example, the lower temperature phase of mono-
(
(
ꢁ ¼ 0:154187 nm). The transmission electron microscopy
TEM) images and selected area electron diffraction (SAED)
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pattern were obtained on a Hitachi H-800 transmission electron
microscope. Scanning electron microscopy (SEM) image
and field emission scanning electron microscopy (FESEM)
image were taken on an X-650 scanning electron microanalyzer
and a JEOL 6700F field emission scanning electron micro-
scope.
clinic Ag2Te is a semiconductor with a narrow band gap in the
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range of 0.04–0.17 eV. Ag2Te undergoes a phase transition to
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the high temperature face centered cubic structure at about
ꢁ
4
þ
145 C. In its high temperature phase, Ag ions are mobile
within a cubic sublattice formed by Te anions, which leads to
Figure 1 shows the typical XRD patterns of the as-prepared
Te fibers and Ag Te fibers. All the diffraction peaks in Figure 1a
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the superionic conductivity. With these properties, silver tel-
luride could be used as good thermoelectric material and prom-
ising material for field sensor.
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can be indexed to the trigonal tellurium with lattice parameters
ꢀ
a ¼ 4:452 and c ¼ 5:921 A, which are in good agreement with
ꢀ
the reported data of a ¼ 4:457 and c ¼ 5:927 A (JCPDS 36-
Bulk Ag2Te was traditionally prepared through a solid reac-
tion between Ag and Te stoichiometrically at high tempera-
1
452). All the reflection peaks in Figure 1b can be indexed to
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the monoclinic Ag Te with lattice parameters a ¼ 8:166,
tures. Ag2Te nanoparticles were also synthesized through soft
chemical methods, such as a room temperature approach for
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ꢀ
b ¼ 4:470, and c ¼ 8:979 A, which are consistent with the re-
ꢀ
ported data of a ¼ 8:164, b ¼ 4:468, and c ¼ 8:977 A (JCPDS
the synthesis of Ag2Te with 5–10% Ag7Te4 reported by Parkin
et al.8,9 One-dimensional (1D) Ag2Te have been reported, in-
cluding Ag2Te nanowires prepared by DC electrodeposition in
65-1104). No obvious reflection peaks for Te can be detected
in Figure 1b.
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porous anodic alumina templates, Ag2Te nanorods obtained
in mixed solvents.11
Herein, we report a useful self-sacrificing template route to
synthesize 1D Ag2Te fibers. Compared with the conventional
hard templates method, self-sacrificing templates used in this
study do not need to be removed after the reaction. The tellurium
fibers used as self-sacrificing templates were first synthesized
through the reduction of Na2TeO4 by hydrazine hydrate; and
the as-prepared tellurium fibers further react with AgNO3 to
get Ag2Te fibers at room temperature.
(
a)
(
b)
Synthesis of Te fibers: analytical grade Na2TeO4 (0.5 mmol)
was first dissolved in 40-mL ethylene glycol to obtain clear solu-
tion. Then 0.6-mL hydrochloric acid (35 wt %) was added, and
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the solution was heated at 80 C under constant stirring for
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20
30
40
50
60
70
min. After cooling to room temperature, 0.5-mL hydrazine hy-
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θ /degree
drate (85 wt % content) was dropped into this solution, and the
solution changed into dark immediately. The resulting solution
was transferred into a 50-mL Teflon-lined stainless steel auto-
clave, which was then sealed and maintained at 100 C for
12 h. After the reaction was completed, the resulting solid prod-
ucts were filtered off, washed with distilled water and absolute
ethanol for several times each, and finally dried at room temper-
ature for 30 min.
Figure 1. XRD patterns of the as-prepared tellurium fibers (a)
and Ag Te fibers (b).
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The panoramic morphology of the freshly synthesized Te
fibers is shown in Figure 2. It can be seen that the sample is
composed of 1D fibers with the diameters ranging from 200 to
800 nm and lengths of tens of micrometers.
Copyright Ó 2005 The Chemical Society of Japan