• Korean Journal of Materials Research
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• v.18 no.9
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• pp.475-481
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• 2008

Positive temperature coefficient of resistivity (PTCR) characteristics of (1-x)$BaTiO_3-x(Bi_{0.5}K_{0.5})TiO_3$ ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free PTC thermistor available at high temperatures of > $120^{\circ}C$. The PTCR characteristics appearing in the ($B_{i0.5}K_{i0.5})TiO_3$ (< 5 mol%) incorporated $BaTiO_3$ ceramics, which might be mainly due to $Bi^{+3}$ ions substituting for $Ba^{+2}$ sites. The 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics showed good PTCR characteristics of a low resistivity at room temperature (${\rho}_r$) of $31{\Omega}{\cdot}cm$ a high ${\rho}_{max}/{\rho}_{min}$ ratio of $5.38{\times}10^3$, and a high resistivity temperature factor (${\alpha}$) of $17.8%/^{\circ}C$. The addition of $Nb_2O_5$ to 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics further improved the PTCR characteristics. Especially, 0.025 mol% $Nb_2O_5$ doped 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics exhibited a significantly increased ${\rho}_{max}/{\rho}_{min}$ ratio of $8.7{\times}10^3$ and a high ${\alpha}$ of $18.6%/^{\circ}C$, along with a high $T_c$ of $148^{\circ}C$ despite a slightly increased ${\rho}_r$ of $31{\Omega}{\cdot}cm$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.6
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• pp.558-566
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• 2003

We fabricated thick film monopole antennas using Li-doped BiNbO$_4$ ceramics and investigated their electrical properties as a function of the Li-doping concentration. Compared with undoped BiNbO$_4$ ceramics, addition of Li$_2$CO$_3$ improved dielectric constant by increasing of ionic polarization, but reduced quality value by increasing of lattice distortion. Antenna properties like gain, bandwidth and radiation patterns were also greatly affected by the addition of Li$_2$CO$_3$. With increasing amount of Li$_2$CO$_3$, the bandwidth of ceramic monopole antenna was increased to 81.7 %, but the gain was reduced to -10.03 dBi. Also radiation patterns were so distorted and showed low dB value by increasing of dielectric loss.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.562-567
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• 2013

A 90 wt% Mg-10 wt% $NbF_5$ sample was prepared by mechanical milling under $H_2$ (reactive mechanical grinding). Its hydriding and dehydriding properties were then examined. Activation of the 90 wt% Mg-10 wt% $NbF_5$ sample was not required. At n=1, the sample absorbed 3.11 wt% H for 2.5 min, 3.55 wt% H for 5 min, 3.86 wt% H for 10 min, and 4.23 wt% H for 30 min at 593K under 12 bar $H_2$. At n=1, the sample desorbed 0.17 wt% H for 5 min, 0.74 wt% H for 10 min, 2.03 wt% H for 30 min, and 2.81 wt% H for 60 min at 593K under 1.0 bar $H_2$. The XRD pattern of the 90 wt% Mg-10 wt% $NbF_5$ after reactive mechanical grinding showed Mg, ${\beta}-MgH_2$ and small amounts of ${\gamma}-MgH_2$, $NbH_2$, $MgF_2$ and $NbF_3$. The XRD pattern of the 90 wt% Mg-10 wt% $NbF_5$ dehydrided at n=3 revealed Mg, ${\beta}-MgH_2$, a small amount of MgO and very small amounts of $MgH_2$ and $NbH_2$. The 90 wt% Mg-10 wt% $NbF_5$ had a higher initial hydriding rate and a larger quantity of hydrogen absorbed for 60 min than the 90 wt% Mg-10 wt% MnO and the 90 wt% Mg-10 wt% $Fe_2O_3$, which were reported to have quite high hydriding rates and/or dehydriding rates. The 90 wt% Mg-10 wt% $NbF_5$ had a higher initial dehydriding rate (after an incubation period) and a larger quantity of hydrogen desorbed for 60 min than the 90 wt% Mg-10 wt% MnO and the 90 wt% Mg-10 wt% $Fe_2O_3$.

• Korean Journal of Materials Research
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• v.29 no.5
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• pp.328-335
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• 2019

Nb-doped $TiO_2$(NTO) coated NiCrAl alloy foam for hydrogen production is prepared using ultrasonic spray pyrolysis deposition(USPD) method. To optimize the size and distribution of NTO particles based on good physical and chemical stability, we synthesize particles by adjusting the weight ratio of the Nb precursor solution(5 wt%, 10 wt% and 15 wt%). The morphological, chemical bonding, and structural properties of the NTO coated NiCrAl alloy foam are investigated by X-ray diffraction(XRD), X-ray photo-electron spectroscopy(XPS), and Field-Emission Scanning Electron Microscopy(FESEM). As a result, the samples of controlled Nb weight ratio exhibit a common diffraction pattern at ${\sim}25.3^{\circ}$, corresponding to the(101) plane, and have chemical bonding(O-Nb=O) at 534 eV. The NTO particles with the optimum weight ratio of N (10 wt%) show a uniform distribution with a size of ~18.2-21.0 nm. In addition, they exhibit the highest corrosion resistance even in the electrochemical stability estimation. As a result, the introduction of NTO coated NiCrAl alloy foam by USPD improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the foam and the electrolyte. Thus, the optimized NTO coating can be proposed for excellent protection of NiCrAl alloy foam for hydrocarbon-based steam methane reforming(SMR).

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.2
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• pp.235-241
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• 1996

In this paper dielectric and electrostrictive strain properties of (1-y-x)Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$$-yPbTiO_{3}-xSrTiO_{3}[(1-y-x)PMN-yPT-xST]$ ceramics fabricated by using columbite precursor method have been investigated with the substitution of SrTiO$_{3}$(ST). Dielectric constant of the specimens increased with the increase of ST content up to 5[m/o] and decreased with further substitution of ST. And the pyrochlore phase decreased with the increase of ST content up to 5[m/o] in XRD analysis. The elimination of the pyrochlore phase improved dielectric constants. The electrostrictive strains generated by AC electric field have the highest value at 5[m/o] SrTiO$_{3}$ addition and the hysteresis of strain ranged from 12 to 20[%]. The electrostrictive strain at various temperature investigated in the temperature range of $-50[^{\circ}C]~74[^{\circ}C].$ In higher temperature than phase transition region, it showed paraelectric property which shows very small hystersis.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.6
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• pp.361-366
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• 2014

$MnO_2$-doped $0.985[Li_{0.04}(Na_{0.545}K_{0.46})_{0.96}(Nb_{0.81}Ta_{0.15}Sb_{0.04})]O_3+0.015KNbO_3(0.985LNKNTS+0.015KNbO_3)$ lead-free ceramics were fabricated by conventional solid state method to develop excellent dielectric and piezoelectric properties. The result of X-ray diffraction patterns obviously indicated that all of the specimen has pure perovskite structure without secondary phase. In addition, orthorhombic phase and coexistance region of orthorhombic-tetragonal phase (MPB) were observed with amount of $MnO_2$. The optimal values of ${\rho}$=4.70 $g/cm^3$, $d_{33}=238$ pC/N, $k_P=0.46$, $Q_m=121$, ${\varepsilon}_r=849$, and $T_C=225^{\circ}C$ were obtained at 0.01 mol% $MnO_2$ doped $0.985LNKNTS+0.015KNbO_3$ ceramics sintered at $990^{\circ}C$ for 5 h, respectively. Hence, it was indicated that the suitable amount of $MnO_2$ could improve the electrical properties of $0.985[Li_{0.04}(Na_{0.545}K_{0.46})_{0.96}(Nb_{0.81}Ta_{0.15}Sb_{0.04})]O_3+0.015KNbO_3$ ceramics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.131-134
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• 2002

The effect of the addition on the densification, low temperature sintering, and microwave dielectric properties of the Ca[($Li_{1/3}Nb_{2/3}$)$_{1-x}$$Ti_{x}$]$O_{3-{\delta}}$/(CLNT) was investigated. $Bi_2O_3$ additives improved the dencification and reduced the sintering temperature from $1150^{\circ}C$ to $900^{\circ}C$ of CLNT microwave dielectric ceramics. As increasing $Bi_2O_3$ contents, the dielectric constants and bulk density were increased. The quality factor, however, was decreased slighty. The temperature coefficients of the resonant frequency shifted positive value as increasing $Bi_2O_3$ contents. The dielectric properties of Ca[($Li_{1/3}Nb_{2/3}$)$_{1-x}$$Ti_{x}$]$O_{3-{\delta}}$ and Ca[($Li_{1/3}Nb_{2/3}$)$_{0.8}Ti_{0.2}$]$O_{3-{\delta}}$ with 5wt% $Bi_2O_3$ sintered at $900^{\circ}C$ for 3h were $\varepsilon_{r}$=20, 35 Q.$f_{0}$=6500, 11,000 GHz, $\tau_{f}$=4, 13 ppm/$^{\circ}C$, respectively.

• Korean Journal of Materials Research
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• v.9 no.5
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• pp.452-459
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• 1999

To develop advanced cladding materials, the effect of Nb addition on the microstructure and corrosion characteristics of Zr-0.8Sn-xNb alloys was investigated. As the Nb content increased, the grain size decreased and the volume fraction of precipitates increased. It was observed from the corrosion test at $360^{\circ}C$ that the corrosion resistance increased with decreasing Nb content. The best corrosion resistance was obtained in Zr-0.8Sn-0.2Nb alloy with high volume fraction of tetra-$ZrO_2$in the oxide. Therefore, it is suggested that Nb in theZr-0.85Sn-xNb system should be added within the solubility limit of Nb from the viewpoint of alloy design.

• Electrical & Electronic Materials
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• v.5 no.1
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• pp.14-27
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• 1992

핫프레스법으로 제작된 0.05Pb(M $n_{1}$3/N $b_{2}$3/) $O_{3}$+ 0.95Pb(Z $r_{0.47}$ $Ti_{0.53}$) $O_{3}$ 세라믹스에 있어서 C $r_{2}$ $O_{3}$의 첨가량이 그 시편의 구조적특성, 유전특성, 압전특성, 온도안정성 및 포아손비에 미치는 영향이 조사되었다. C $r_{2}$ $O_{3}$의 첨가량의 범위가 0.3~0/75[wt%]인 시편만이 포아손비가 1/3이상으로 주파수저하형 에너지포획소자의 기판으로 사용될 수 있으며 이 중에서 C $r_{2}$ $O_{3}$의 첨가량이 0.5[wt%]인 시편이 보다 우수한 압전특성과 안정된 주파수 온도특성을 갖고 있다. 있다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.1
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• pp.38-42
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• 2005

B$_2$O$_3$ added Ba(Mg$_{1}$3/Nb$_{2}$3/)O$_3$ (BBMN) ceramics were not sintered below 900 $^{\circ}C$. However, when CuO was added to the BBMN ceramic, it was sintered even at 850 $^{\circ}C$. The amount of the $Ba_2$B$_2$O$_{5}$ second phase decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B$_2$O$_3$ inhibiting the reaction between B$_2$O$_3$ and BaO. Moreover, it is suggested that the solid solution of CuO and B$_2$O$_3$ might be responsible for the decrease of the sintering temperature of the specimens. A dense microstructure without pores was developed with the addition of a small amount of CuO. However, a porous microstructure with large pores was formed when a large amount of CuO was added. The bulk density, the dielectric constant ($\varepsilon$$_{r}$) and the Q-value increased with the addition of CuO but they decreased when a large amount of CuO was added. The variations of those properties are closely related to the variation of the microstructure. The excellent microwave dielectric properties of Qxf = 21500 GHz, $\varepsilon$$_{r}$ = 31 and temperature coefficient of resonance frequency($\tau$$_{f}$) = 21.3 ppm/$^{\circ}C$ were obtained for the Ba(Mg$_{1}$3/Nb$_{2}$3/)O$_3$+2.0 mol%B$_2$O$_3$+10.0 mol%CuO ceramic sintered at 875 $^{\circ}C$ for 2 h.h.2 h.h.