• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1420-1421
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• 2006

In this study, structural and micowave dielectric properties of the $Mg_{5}B_{4}O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceeramics. The specimens are prepared through the solid-state route. According to the XRD pattern, $Mg_{4}Ta_{2}O_9$ and $MgTa_{2}O_6$ phase exist in calcined and sintered $Mg_{5}Ta_{4}O_{15}$ powder. Also $Mg_{5}Ta_{4}O_{15}$ phase added with increasing sintering temperature. In the case of calcined and sintered $Mg_{5}Nb_{4}O_{15}$ powder, single phase of $Mg_{5}Nb_{4}O_{15}$ were appeared. The bulk density and quality factor of the $Mg_{5}B_{4}O_{15}$ (B=Ta, Nb) ceramics were increased with sinteming temperature in $1400^{\circ}C{\sim}1450^{\circ}C$, but these were decreased in another sintering temperature. Dielectric constant of the $Mg_{5}Ta_{4}O_{15}$ ceramics was increased continuously with increasing of sintering temperature. And the dielectric constant of the $Mg_{5}Nb_{4}O_{15}$ ceramics was increased in $1400^{\circ}C{\sim}1450^{\circ}C$ but decreased in $1475^{\circ}C$. In the case of the $Mg_{5}Ta_{4}O_{15}$ and $Mg_{5}Nb_{4}O_{15}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, -10.91 $ppm/^{\circ}C$ and 14, 37,350 GHz, -52.3 $ppm/^{\circ}C$, respectively.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.7
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• pp.347-351
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• 2004

The $ZnNb_2O_{6}$ ceramics with CuO(1, 3, 5wt%) were prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of $950^{\circ}C$∼$1075^{\circ}C$ for 3hr in air The structural properties and the microwave dielectric properties of $ZnNb_2O_{6}$ ceramics were investigated with sintering temperature and the addition of CuO. Increasing the addition of CuO, the peak of second phase($Cu_3Nb_2O_{8}$) was increased. The grain size of the $ZnNb_2O_{6}$ ceramics with CuO was increased with CuO addition at same temperature. The dielectric constant of $ZnNb_2O_{6}$ ceramics with CuO was increased with sintering temperature and CuO addition. While the quality factor of the $ZnNb_2O_{6}$ ceramics with lwt% CuO depended on sinterability, the quality factor of $ZnNb_2O_{6}$ with 3wt% and 5wt% CuO depended on second Phase due to the CuO addition. The optimum dielectric Properties of $\varepsilon$$_{r}$ = 21.73 Q${\times}$f = 19,276 were obtained from the condition of 3wt% CuO addition and sintering temperature of $1025^{\circ}C$(3hr).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.260-260
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• 2007

강유전성 세라믹스 재료로써는 PZT계열의 세라믹재료가 널리 쓰이고 있다. 이는 우수한 유전 및 압전특성을 가지고 있으나, PbO을 다량 함유하고 있어 $1000^{\circ}C$이상에서 PbO가 급격하게 휘발되는 성질에 따라서 조성의 변동이 생겨 재현성이 어려우며 이를 방지하기 위하여 과잉 PbO를 첨가시키기 때문에 PbO휘발로 인한 강한 독성이 인체에 유해하다. 최근에는 Pb의 환경문제가 대두됨에 따라 이를 대체할 다른 물질의 개발이 활발하게 연구되고 있다. 대표적인 비납계 강유전 세라믹스인 $(Na_{0.5}K_{0.5})NbO_3$ ($d_{33}$ = 120 pC/N, Kp = 39%, Qm = 210, 이하 NKN라 표기) 조성은 $KNbO_3,\;NaNbO_3$ 상태도에 따라 순수한 NKN 세라믹스는 $1140^{\circ}C$에서 안정상을 가지나, 높은 온도로 인하여$Na_2O$와 $K_2O$가 쉽게 휘발됨에 따라 화학량 비의 변화가 생겨 이차 상을 형성하기도 한다. 따라서 본 연구에서는 $LiNbO_3$의 새로운 고용체를 추가시켜 기본 NKN조성에 압전성 및 고온에서의 상안정성을 향상시키고자 하였다. 최적 조성을 설계하기 위하여 (1-x)$(Na_{0.5}K_{0.5})NbO_3-xLiNbO_3$, x=(0,0.02,0.04,0.06,0.08)의 범위에서 조성을 변화시키면서 실험하였다. 시편 제작은 일반적인 세라믹스 소결 공정을 적용하였는데, $850^{\circ}C$에서 5시간 하소 후 $1080^{\circ}C$에서 2시간 소결하였다. 하소 및 소결 후에는 XRD분석을 통해 perovskite구조를 확인하였고, 미세구조 확인을 위해 주사전자현미경 (SEM)으로 관찰하였다. 압전특성을 평가하기 위해 압전 $d_{33}$-meter를 사용하였으며, impedance analyzer (HP 4194A)를 이용하여 전기적 특성을 측정하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.172-173
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• 2008

In this study, $0.95(K_{0.5}Na_{0.5})NbO_3$-0.05Li$(Sb_{0.8}Nb_{0.2})O_3$ + $Ag_2O$ + x wt% $MnO_2$ were investigated as a function of the amount of $MnO_2$ addition in order to improve dielectric and piezoelectric properties of Lead-free piezoelectric ceramics. With increasing the amount of $MnO_2$ addition, density and electromechanical coupling factor $(k_p)$ increased up to 0.3wt.% $MnO_2$ and decreased above 0.3wt.% $MnO_2$. At the sintering temperature of 1020 $^{\circ}C$, Electromechanical coupling factor $(k_p)$, density, dielectric constant $({\varepsilon}r)$ and mechanical quality factor $(Q_m)$ of composition ceramics with 0.4wt% $Ag_2O$ addition showed the optimal value of 0.431, 4.33 g/$cm^3$, 820 and 119, respectively.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1885-1887
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• 1999

본 연구에서는 $BaTiO_3$를 기본조성으로하는 반도성 세라믹스인 PTC 써미스터에 $Nb_2O_5$을 미량 첨가하여 미세구조 및 PTCR의 전기적 특성에 대해서 연구하였다. 또한 복소 임피던스 측정을 통하여 $Nb_2O_5$ 첨가에 따른 grain, grain boundary 저항변화에 대해서도 고찰하였다. $(Ba_{0.9}Sr_{0.05}Ca_{0.05})TiO_3-0.01SiO_2-0.001MnCO_3$를 기본조성으로 하여 $Nb_2O_5$ 첨가량을 $0.15{\sim}0.2mol%$까지 변화시켰으며 소결조건은 소결온도 $1350^{\circ}C$, 2h 유지하였으며 냉각속도는 $100^{\circ}C/h$로 하였다 첨가된 Nb의 양이 증가할수록 grain의 크기는 점차로 작아졌으며 상온저항과 peak 저항이 함께 증가하였다. 0.15mol% 첨가된 시편의 경우 상온저항은 $19[\Omega]$이었으며 peak 저항은 $5{\times}10^6[{\Omega}]$정도가 되었다.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.

• Transactions on Electrical and Electronic Materials
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• v.14 no.6
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• pp.312-316
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• 2013

In this study, short-circuit preventive layer (blocking layer) was deposited between conductive transparent electrode and porous $TiO_2$ film in the DSSCs. As blocking layer, we selected the metal-oxide such as $TiO_2$, $Nb_2O_5$ and ZnO. The sheet resistance with each different blocking layers were 18 ${\Omega}/sq.$ for the $TiO_2$, 10 ${\Omega}/sq.$ for the $Nb_2O_5$ and 8 ${\Omega}/sq.$ for the ZnO, while the RMS (Root Mean Square) roughness value of DSSCs were 39.61 nm for the $TiO_2$, 41.84 nm for the $Nb_2O_5$ and 36.14 nm for the ZnO respectively. From the results of photocurrent-voltage curves, a sputtered $Nb_2O_5$ blocking layer showed higher performance on 2.64% of photo-electrochemical properties. The maximum of conversion efficiency which was achieved under 1 sun irradiation by depositing the blocking layer increased up to 0.56%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.925-929
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• 2009

In this study, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3$ ceramics were investigated as a function of the amount of $Ag_2O$ addition in order to improve dielectric and piezoelectric properties of lead-free piezoelectric ceramics. With increasing the amount of $Ag_2O$ addition, density and electromechanical coupling factor ($k_p$) increased up to 0.2 wt.% $Ag_2O$ and decreased above 0.2 wt.% $Ag_2O$. At the sintering temperature of $1020^{\circ}C$, electromechanical coupling factor ($k_p$), density, dielectric constant (${\varepsilon}r$) and curie temperature (Tc) of ceramics with 0.2 wt% $Ag_2O$ showed the optimal values of 0.42, $4.33\;g/cm^3$, 738 and $393^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.11
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• pp.926-931
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• 2000

The microwave dielectric properties and the microstructures as a mole fraction of (1-x)ZnNb$_2$O$_{6}$-xPb$_{5}$Nb$_4$O$_{15}$ ceramics with CuV$_2$O$_{6}$, Sb$_2$O$_3$ and glass(ZNPN ceramics) was investigated. 0.98ZN-0.02PN ceramics containing 1.5 wt% CuV$_2$O$_{6}$ 1.0 wt% Sb$_2$O$_3$ and 1.0 wt% glass had a dielectric constant($\varepsilon$$_{r}$) of 23, Qxf$_{o}$ value of 15000 and TCF(Temperature Coefficient of resonance Frequency) of -25 ppm/$^{\circ}C$ and it is possible to be co-fired with Ag electrode at 90$0^{\circ}C$. As sintered temperature increases over 90$0^{\circ}C$ the grain size of ZNPN ceramics was increasing for growth and it has poor co-fired properties with Ag electrode.e.ctrode.e.e.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.260-260
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• 2007

Low-temperature sintering and dielectric properties of the $1-xBiNbO_4-xZnNb_2O_6$ ceramics (x=0.3, 0.5, and 0.7) with 10 wt% zinc borosilicate (ZBS) glass was investigated as a function of the substitution of $ZnNb_2O_6$ with a view to applying this system to LTCC technology. The all composition addition of 10 wt% ZBS glass ensured a successful sintering below $900^{\circ}C$. The the amount of $ZnNb_2O_6$ on $ZnNb_2O_6$ ceramics increased the $Q{\times}f$ values, but it decreased the sinterability and dielectric constant due to the higher $Q{\times}f$ value and sintering temperature of $ZnNb_2O_6$ than that of $ZnNb_2O_6$ ceramics. The increase of $ZnNb_2O_6$ content from 0.3 to 0.7 in the $1-xBiNbO_4-xZnNb_2O_6$ ceramics with 10 wt% ZBS glass sintered at $900^{\circ}C$ demonstrated 30~20 in the dielectric constant (${\varepsilon}_r$), 3,500~4,500 GHz in the $Q{\times}f$ value.