• 한국전기전자재료학회논문지
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• 제25권8호
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• pp.602-610
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• 2012

The powders for the $Na_xWO_3$ (x= 1 and 0.75) sputtering targets were synthesized by the calcination in reductive atmosphere. Near single-phase $NaWO_3$ and single-phase $Na_{0.75}WO_3$ powder targets were prepared. By using the targets, thin films of each composition were deposited by rf magnetron sputtering on the $SiO_2$ (100 nm)/Si substrates and annealed by RTP (rapid thermal processing) for crystallization. In the case of the $NaWO_3$ composition, single-phase $Na_xWO_3$ thin films, where x was believed to be slightly less than 1, were fabricated accompanying the Na-diffusion into the substrates during RTP. However, in the case of the $Na_{0.75}WO_3$ thin film preparation, it was unable to make single-phase thin films. From the phase formation behaviors of both powders and thin films, it was revealed that $Na_xWO_3$ with nonstoichiometric composition of x, which was slightly less than 1, was favorable. The good electrical conduction properties were obtained from the single-phase $Na_xWO_3$ thin films. Their electrical resistivities were as low as $7.5{\times}10^{-4}{\Omega}{\cdot}cm$.

• 한국재료학회지
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• 제23권9호
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• pp.537-542
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• 2013

Two types of Tb- and Na-substituted green phosphors $Ca_{(1-1.5x)}WO_4:Tb_x^{3+}$: and $Ca_{(1-2x)}WO_4:Tb_x^{3+},Na_x^+$ were synthesized with various x values, using a solid-state reaction. The former phosphors contained both substitutional and vacancy point defects, while the later had only substitutional defects. X-ray diffraction results showed that the main diffraction peak, (112), was centered at $2{\theta}=28.72^{\circ}$ and indicated that there was no basic structural deformation caused by substitutions or vacancies. The photoluminescence emission and photoluminescence excitation spectra revealed the optical properties of trivalent terbium ions, $Tb^{3+}$. Typical transitions, $^5D_3{\rightarrow}^7F_6,\;^7F_5,\;^7F_4$ and $^5D_4{\rightarrow}^7F_6,\;^7F_5,\;^7F_4,\;^7F_3$, and cross relaxations were observed. Subtle differences in the photoluminescence of green phosphors were observed as a result of the point defects. The FT-IR spectra indicated that some of the ungerade vibrational modes had shifted positions and changed shapes, spreading out over a wide range of frequencies. This change can be attributed to the different masses of $Tb^{3+}$ and $Na^+$ ions and $V_{Ca}$" vacancies compared to $Ca^{2+}$ ions. The gerade normal modes of the Raman spectra exhibited subtle differences resulting from point defects in $Ca_{(1-1.5x)}Tb_xWO_4$ and $Ca_{(1-2x)}Tb_xNa_xWO_4$.

• Bulletin of the Korean Chemical Society
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• 제34권9호
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• pp.2769-2773
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• 2013

Red phosphors $Ca_{(1-1.5x)}Eu_xWO_4$ and $Ca_{(1-2x)}Eu^_xNa_xWO_4$ were synthesized with various concentrations x of $Eu^{3+}$ ions by using a solid-state reaction method. The crystal structure of the red phosphors were found to be a tetragonal scheelite structure with space group $I4_1/a$. X-ray diffraction (XRD) results show the (112) main diffraction peak centered at $2{\theta}=28.71^{\circ}$, and indicate that there is no basic structural deformation caused by the vacancies ${V_{Ca}}^{{\prime}{\prime}}$ or the $Eu^{3+}$ (and $Na^+$) ions in the host crystals. Densities of $Ca_{(1-1.5x)}Eu_xWO_4$ were measured on a (helium) gas pycnometer. Comparative results between the experimental and theoretical densities reveal that $Eu^{3+}$ (and $Na^+$) ions replace the $Ca^{2+}$ ions in the host $CaWO_4$. Also, the photoluminescence (PL) emission and photoluminescence excitation (PLE) spectra show the optical properties of trivalent $Eu^{3+}$ ions, not of divalent $Eu^{2+}$. Raman spectra exhibit that, without showing any difference before and after the doping of activators to the host material $CaWO_4$, all the gerade normal modes occur at the identical frequencies with the same shapes and weaker intensities after the substitution. However, the FT-IR spectra show that some of the ungerade normal modes have shifted positions and different shapes, caused by different masses of $Eu^{3+}$ ions (or $Na^+$ ions, or ${V_{Ca}}^{{\prime}{\prime}}$ vacancies) from $Ca^{2+}$.

• 한국결정학회지
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• 제10권2호
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• pp.110-113
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• 1999

x의 범위가 0.5

• The Korean Journal of Ceramics
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• 제2권3호
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• pp.157-161
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• 1996

Cry structures of $Na_xWO_3$ (0.5$\leq$x$\leq$1.0) were investigated. Transmission electron microscopy (TEM) studies indicate that there is an ordering of sodium ions when x=0.75. The direction of ordering is [110] and the wavelength of ordering is twice of the interplanar distance of (110) plane. It has been confirmed that a superlattice containing eight $Na_{0.75}WO_3$ is the unit cell of ordered structure. In this unit cell, Na sites at (000) and ($\frac{2}{1}\frac{2}{1}\frac{2}{1}$) are vacant. The ordered phase was preserved after the annealing at $600^{\circ}C$ in the air. In reduced $Na_xWO_3$ with x=0.5 and 1.0, extra phases were found with the partially ordered perovskite phase. After annealing at $600^{\circ}C$, theses phases transformed to the phases found in calcined specimens.

• Bulletin of the Korean Chemical Society
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• 제34권3호
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• pp.731-734
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• 2013

Reduced tungsten bronze nanoparticles of ternary and quaternary compounds were prepared by adding sodium and cesium to crystal structures of tungsten trioxides ($Na_xCs_{0.33-x}WO_3$, x = 0, 0.11) while maintaining the overall alkali metal fraction at 0.33, in an attempt to control near infrared (NIR) shielding property in the particular wavelength range of 780 to 1200 nm. The structure and composition analysis of the quaternary compound, $Na_{0.11}Cs_{0.22}WO_3$, revealed that 93.1% of the hexagonal phase was formed, suggesting that both alkali metals were mainly inserted in hexagonal channel. The NIR shielding property for $Na_{0.11}Cs_{0.22}WO_3$ was remarkable, as this material demonstrated efficient transmittance of visible light up to 780 nm and enhancement in NIR shielding because of the blue-shifted absorption maximum in comparison to $Cs_{0.33}WO_3$.

• 한국전기전자재료학회논문지
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• 제27권8호
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• pp.510-515
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• 2014

Thin films of cubic $Na_{0.6}WO_3$, which is one of the sodium tungsten bronze, were fabricated by rf sputtering for the electrode applications in integrated sensors and actuators. A single-phase cubic $Na_{0.6}WO_3$ sputtering target of power type was prepared by conventional solid-state reaction. Thin films were deposited from the powder target, and the as-deposited films were amorphous, thus they annealed by tube furnace or RTP for crystallization. Thin films having cubic phase $Na_xWO_3$ were fabricated by the optimization of sputtering and post-annealing conditions, but single-phase cubic $Na_{0.6}WO_3$ thin films were not obtained. Although the films were not in single phase, they had good electrical conduction properties showing electrical resistivities of $10-4{\Omega}{\cdot}cm$ order.

• 전기화학회지
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• 제8권1호
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• pp.32-36
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• 2005

본 연구는 $WO_3$ 박막과 $NiO-WO_3$ 박막을 고진공 저항가열식 thermal evaporation 법으로 (100) n형의 실리콘 단결정 기판 위에 증착시켰고, 막의 결정성 증진을 위하여 공기 중 $500^{\circ}C$에서 30분 동안 열처리하였다. 박막의 결정성 및 결정구조를 분석하기 위해서 X선 회절분석기를 사용하였고, 표면 및 단면 관찰을 위해서는 주사전자현미경을 이용하였다. 그리고 화학 조성 결합에너지는 XPS를 이용하였다. 순수 $WO_3$ 박막의 결정 크기는 $500^{\circ}C$에서 30분 동안 공기중 열처리에 의해서 $0.6{\mu}m$로 성장하였고 $WO_3$ 박막의 두께가 증가할수록 거의 변화 없이 일정하였다. 반면, NiO가 첨가된 $WO_3$ 박막 두께별 결정크기는 각각 $0.12{\mu}m,\;0.28{\mu}m,\;0.32{\mu}m$및 $0.43{\mu}m$로 순수 $WO_3$ 박막에 비해 치밀한 표면을 형성하였고, 최대 5배정도 성장이 억제되었다. 가스감도 측정은 대기 중에서의 센서 저항 값을 기준으로 측정가스 저항 값의 비율 $(R_{NOx}/R_{air})$로 가스감도를 나타내었다. 전기적 성질은 MFC로 NOx가스 5ppm을 일정히 유지시켰고, Multimeter로 계측하여 컴퓨터에 자동 계측되는 시스템을 사용하였다. 순수 $WO_3$박막보다는 $NiO-WO_3$ 박막이 우수한 NOx 감도특성을 보였고 센서의 작동온도는 $250^{\circ}C$에서 우수한 감도를 나타내었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.220-220
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• 2016

본 연구에서는 녹황색 빛을 내는 NaY(WO4)2:Tb3+ 형광체 파우더를 하소 350도에 1시간 소결 950도에 4시간 고상반응법으로 합성하였으며, 파우더는 X-ray diffraction과 PL 장비를 이용하여 측정하였다. XRD 분석은 Tb3+이온 도핑농도에 의한 순수한 NaYWO4 상을 나타내었다. Fig.1 220-330nm에서 관찰되는 넓은 밴드는 $O2-{\rightarrow}W6+$에 의해 발생한 LMCT(ligand to metal charge transfer)이고, Tb3+에서 WO42-그룹으로 에너지 전달에 의해서 생긴다. 이것의 최대세기는 272nm 이다. LMCT 옆 330-390nm에 관찰되어지는 약한 강도와 넓은 밴드는 Tb3+ 4f8의 f-f transition에 의해 발생한다. Fig.2에서 보여 지듯이$ 5D4{\rightarrow}7F6$, 7F5, 7F4, 7F3는 파장 489nm, main peak인 545nm (Green,초록색), 588nm (orange, 주황색), 620nm (Red, 적색)에서 Peak가 나타났으며, Tb3+이온의 함량비가 0.08mol일 때 최대 발광이 관측 되었다.

• 한국세라믹학회지
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• 제52권1호
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• pp.66-71
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• 2015

$NaY_{1-x}(WO_4)_2:Ho^{3+}/Yb^{3+}$ phosphors with doping concentrations of $Ho^{3+}$ and $Yb^{3+}$ ($x=Ho^{3+}+Yb^{3+}$, $Ho^{3+}=0.05$, 0.1, 0.2, and $Yb^{3+}=0.2$, 0.45) were successfully synthesized via the cyclic microwave-modified sol-gel route; their upconversion properties were investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, the synthesized particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a very strong 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the domination of strong peaks at higher and lower frequencies induced by the incorporation of the $Ho^{3+}$ and $Yb^{3+}$ elements into the $Y^{3+}$ sites in the crystal lattice, which resulted in unit cell shrinkage that accompanied a new phase formation of the $WO_{4-x}$ group.