2012 3rd International Conference on Biology, Environment and Chemistry
IPCBEE vol.46 (2012) © (2012) IACSIT Press, Singapore
DOI: 10.7763/IPCBEE. 2012. V46. 9
Effect of CsxWO3 Nanoparticles Content and Atomic Ratio for Near
Infrared Cut-off Characteristics
Jae young Kim, Hyun Jin Yoon, Seung yong Jeong, Sangkug Lee, Gyo jic Shin and Kyung Ho Choi
Center for Green Materials Technology, Korea Institute of Industrial Technology, 35-3, Hongcheon-ri,
Ipjang-myeon, Seobukgu, Cheonan-si, Chungnam-do 330-825, Republic of Korea
Abstract. In this work, the ceramic nanocomposites films with homogeneous dispersions of tungsten
bronze nanoparticles with ternary additive cesium have been prepared by mixing Urethane acrylic/UVcoating binder and dispersed sol depending on the atomic ratio and the particle contents. Furthermore, we are
synthesized the CsxWO3 with different annealing at 700, 800, and 900 ℃ in an N2 gas for 1 hr respectively.
The structure and sizes of ceramic particles was observed XRD and PSA spectrometer, the heat-shielding
properties of their films were investigated by NIR spectrometer. Synthesized Cs0.33WO3 particles with
annealing at 800 ℃ typically formed hexagonal tungsten bronze structure for good absorption of NIR, size
observed as being 30-100 nm and <150 nm. Especially, remarkable absorption of NIR wavelength ranges
makes ceramic composite films good candidate for use as a heat shielding window, it clearly shows useful for
applications where heat shield is required.
Keywords: Caesium, Nanoparticles, NIR, Hexagonal, Heat-shielding.
1. Introduction
The various nanoparticles have been investigating the continuous and new methods to reduce solar heat
as it ensures a potentially low-cost and high-productivity solution. Not only does it needs high transmittance
of ultraviolet radiation but also achieves complete shielding of infrared solar radiation can be used for solar
control windows. In the other word, an effective IR absorbent should have high absorbance as well as a
broad working wavelength. A well known the kinds of materials to realize the purpose is the nanoparticles of
transparent oxide conductors with heat-ray cut-off effect such as tin doped indium oxide (ITO) and antimony
doped tin oxide (ATO). They also are well known to provide highly transparent solar filters to absorb heatray by the effect of the plasma vibration of the free electrons, as typically observed in gold and silver
nanoparticle solution. However, ITO can only shield the IR wavelength ranges longer than 1500 nm as well
as indium is an expensive metal resource. In recent years, for practical application, tungsten bronzes actively
have been investigating due to their interesting electro-optics, photochromic, electrochromic, and
superconducting properties. Tungsten trioxide (WO3) has a wide band gap of 2.6-2.8 eV5 and is transparent
in the visible and NIR ranges. A metallic conductivity and a strong NIR wavelength absorption can be
induced when free electrons are introduced into crystals by either decreasing the oxygen content or by
adding ternary elements. The oxygen deficiency in tungsten oxides leads to a complex-ordered structure
known as the Magneli structure, while the ternary addition of the positive ions leads to the tungsten bronze
structure. In other words, tungsten bronzes MxWO3 with doping small ions such as H+, Ag+, Li+, Na+, K+ and
Cs+ into WO3 have better optical and electrical properties. It has been reported that the tungsten bronzes with
the hexagonal phase are of particular interest in the application of electrochromic devices owing to the
relatively high diffusion coefficients of hydrogen ions and metal ions compared with those of the
orthorhombic phase and pure WO3.
On the other hand, as for the Cs-doped WO3, the superconductivity of CsxWO3 prepared by reported that
CsxWO3 with 0.3 ≥ x ≥ 0.19 was a 3D superconductor, a transition from a metal to an insulator occurs at x <
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0.19, and a 2D superconductor was formed at x=0.05. In addition to, the hexagonal tungsten bronze phase of
Cs0.33WO3 was regarded as being highly attractive in solar filter applications because of its strong absorption
in the NIR wavelengths.
The traditional methods for preparing the hexagonal tungsten bronze CsxWO3 usually require high
temperature and harsh reaction conditions, such as heating mixtures of WO3 with K, Rb or Cs salts in
reducing atmospheres at 1000 ℃. Recently, morphology and phase control of particles by soft chemical
synthesis methods have attracted wide interest in the synthesis of many oxides such as ZnO, WO3, etc. It has
been acknowledged that the microstructure and morphology of particles play an important role in its
properties. Up to now, synthesizing pure WO3 with different morphologies and properties has been widely
reported. However, there is limited work reported on the synthesis and characterization of CsxWO3 with
controlled morphology by solvothermal reaction. Furthermore, the effects of ammonia annealing on the heatshielding properties of CsxWO3 have not been reported.
In this paper, we synthesized the caesium doped tungsten tri-oxide (Cs0.33WO3) nanoparticle with the
different annealing temperature, various concentration and controlled atomic ratio by using the traditional
solid state reaction method and investigated the their morphological properties and the optical properties of
nanoceramic composite films for solar light control applications.
2. Experimentals
Synthesizing of homogenous CsxWO3 powder, Cs2CO3 of various concentration and H8MoN2O4 were
mixed in aqueous, dried at 180 ℃ for 8 hr. The precursor as dried at 180 ℃ was heated in a tubular furnace
at 450 ℃ for 1 hr with H2/N2 gas flow at H2/N2=90/10, followed by annealing at 800 ℃ in an N2 gas for 0.5
hr. The as-produced powders were dispersed by turbomill with iron ball for 2hr and the zirconia bead for 1 hr
respectively. In the other hand, nanocomposite films were prepared with mixing urethane acrylic/UV coating
binder and well dispersed perovskites sol by using bar coater. Dispersion and coating binder were mixed well
in vial with rotating mixer. The prepared films were dried at 80 ℃ for 1min in heating chamber and
illuminated with a mercury UV lamp UV-curing equipment at intensity 800 W/cm for 20 sec. The structure
and sizes of synthesized perovskite particles was observed XRD and PSA spectrometer, the optical
properties of their composite films were investigated by UV-VIS and NIR spectrometer. The synthesis of
products is summarized outlined in Scheme1.
Scheme 1. Synthetic scheme of the nanoparticles and theirs composite films.
3. Results and Discussion
Figure 1 exhibits the typical XRD patterns of the synthesized Cs0.33WO3 particles with the different
annealing temperatures. All peaks could be indexed to the hexagonal cesium tungsten bronze (JCPDS No.
831334) and the only Cs0.33WO3 particle synthesized in annealing at 800 ℃ almost was identified to
disappear the impurity peak. It can be seen that the nanoparticles obtained by annealing at 800 ℃ prefers the
hexagonal tungsten bronze structure. It was well known that the relatively larger ions such as Ti (0.150 nm),
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Rb (0.152 nm), and Cs (0.170 nm) compared with Li, Na etc. could fit better in the hexagonal vacant tunnels
(0.163 nm) in the hexagonal tungsten bronze structure rather than in the rectangular vacant tunnels in the
cubic tungsten bronze structure. In the other hand, this result suggested that the typical hexagonal structure
of Cs0.33WO3 with remarkable absorption of NIR was formed by annealing at 800 ℃.
Annealing - 700
Annealing - 800
Annealing - 900
Ref.
0
20
40
60
80
100
2theta scale
Fig. 1: XRD patterns of CsxWO3 particles synthesized in different annealing temperature.
Fig. 2: Shows the typical SEM image of synthesized Cs0.33WO3 particle by 800 ℃ annealing temperature.
A synthesis of Cs0.33WO3 particle with annealing temperature of 800℃ was morphology as measured by
SEM. The Cs0.33WO3 particle under the 100 nm can be observed in Fig. 2. Each Cs0.33WO3 particle was
aggregated with the mass of the few micron size. Those clusters shatter to pieces by pulverization dispersed
methods. These results agree well with the XRD profiles of the samples shown in Fig. 1.
Figure 3 exhibits the properties of NIR absorption with different annealing temperature. These results
indicated that the NIR absorption properties sensitively depended on the annealing temperature of Cs0.33WO3
particle. As above mentioned, it means that the effective absorption of NIR range for Cs0.33WO3 composite
films increase with increasing content of hexagonal tungsten bronze structure of Cs0.33WO3. This is
consistent well with the XRD profiles of the samples shown in Fig. 1.
Fig. 3: NIR transmittance spectra of Cs0.33WO3 (1.5 wt%) particle with different annealing temperature.
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Figure 4 shows the properties of NIR absorption of CsxWO3 with annealing at 800 ℃. As the atomic
ratio (from 0.33 to 1.00) of CsxWO3 increased, only NIR transmittance of Cs0.33WO3 and Cs0.55WO3
significantly was decreased while the other sample is not changes the NIR transmittances. As above
mentioned, this result implied that only Cs0.33WO3 was formed the typical hexagonal tungsten bronze
structure with superior absorption of NIR wavelength.
Fig. 4: NIR transmittance spectra of CsxWO3 (1.5 wt%) composite films with different atomic ratio (annealing
temperature 800 ℃).
Figure 5 represented the relation between NIR shielding effect and Cs0.33WO3 concentrations. According
to the illustration, As the Cs0.33WO3 concentration increased from 0.5, 1.0, 1.5 and 2.5 wt%, NIR
transmittance value commonly were declined whereas NIR transmittance increased with increasing x values
of Cs0.33WO3. Particularly, in case of Cs0.33WO3 clearly indicated that the distinct absorption curve around
1000 nm. This discrepancy could be explained by an underestimation of short-range order effects in the XRD
pattern whereas in IT phonon absorption short-range-order effects are seen mainly. Single-phase hexagonal
tungsten bronze (x=0.33) only possess a clear increase in absorption that increases with increasing contents.
As a result, this suggests that the properties of NIR absorption subtly depended on the annealing temperature,
content and composition(x content) of Cs0.33WO3.
Fig. 5: NIR transmittance spectra of films containing various concentration of Cs0.33WO3 (1.5 wt%) particle (annealing
temperature 800 ℃).
Because the perovskites-based nanomaterials exhibit strong absorption of NIR wavelength, it is expected
to convert the absorbed radiation to local heat directly to phototherrmal conversion properties of the
nanomaterials, the prepared composite film were put on a paper and then irradiated by a 250 W IR lamp for
30 s. The temperature distribution was recorded by thermographic analysis. Figure 6 shows the image of
Cs0.33WO3 composite film. The measurement was performed at an ambient temperature of 25 °C. Within only
20 s, the temperature of the composite film increased from 25 to 135 °C, whereas the temperature of the
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other around the composite film did not rise very much, indicating the quick conversion of absorbed NIR
wavelength energy to local heating energy on the composite film.
Fig. 6: Thermographic images of the Cs0.33WO3 nanoparticles (irradiation by a 250 W IR lamp).
4. Conclusion
In this study, we synthesized the homogeneous cesium tungsten bronze nanoparticles by using traditional
solid state reaction method with changing reaction condition and investigated the heat-shielding properties of
their composite films. It can be confirmed that only the Cs0.33WO3 nanoparticles mainly has the hexagonal
tungsten bronze structure by annealing at 800 ℃, size of CsxWO3 observed as being 30~100 nm and ≤ 150
nm. In the other hand, the Cs0.33WO3 nanoparticle observed at the 75 nm and was aggregated with the mass
of the few micron size. All synthesized nanoparticles exhibited the properties of NIR shielding. Particularly,
the nanoparticle of Cs0.33WO3 synthesized by the annealing at 800 ℃ showed a pronounced absorption of
NIR light transmittance. Due to thermographic analysis of IR light, the Cs0.33WO3 nanoparticle thin film cut
off the NIR radiation mainly by absorption.
5. References
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nanoparticle dispersions. 2007, 90: 4059.
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and Tsugio Sato. Microstructure and electrical-optical properties of cesium tungsten oxides synthesized by
solvothermal reaction followed by ammonia annealing. Journal of Solid State Chemistry. 2010, 183: 2456.
[3] Guo, Shu Yin, Lijun Huang, Lu Yang, and Tsugio Sato. Effects of Crystallization Atmospheres on the
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[4] Chongshen Guo, Shu Yin, Mei Yan, and Tsugio Sato. Facile synthesis of homogeneous CsxWO3 nanorods with
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