• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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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.

• 한국재료학회지
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• 제4권7호
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• pp.798-807
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• 1994

$BaTio_{3}$에 Ca가 첨가되면 상온 저항을 증가시키며 이는 $Ca^{2+}$가 $Ti^{4+}$를 치환하여 acceptor 불순물을 형성하기 때문이라고 생각된다. 그러나 $Ca^{2+}$는 $Ti^{4+}$보다 이온 반경이 크므로 그 자리를 치환하지 않는다는 주장도 있다. 본 실험에서는 $BaTiO_{3}$에 의한 acceptor가 존재하는지 알아보기 위하여 Ba/(Ti+Ca+Nb)=1이 되도록 Ca와 Nb를 첨가하여 산소 분압의 변화에 따른 고온 평형 전기 전도도를 측정하였다. 측정은 $1000^{\circ}C$에서 행하였으며 산소 분압은 $10^{-15}$ ~ 1 기압의 범위에서 조절하였다. 첨가된 Ca와 Nb의 농도를 변화시킨 결과, acceptor와 donor의 상호 보상 효과가 나타났다. 즉, Nb에 의한 donor를 보상하는 acceptor가 존재함을 확일하였고, 전도도 곡선의 결함 화학적인 해석에 의하여 Ca가 Ti자리를 치환함을 알았다. 이러한 acceptor의 존재는 ICTS에 의해서도 확인되었다.

• 전기전자학회논문지
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• 제23권2호
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• pp.538-542
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• 2019

광 전환 효율에 관여하는 $TiO_2$와 같은 반도체 산화물은 염료 감응 태양전지(Dye-sensitized solar cell, DSSC)의 주요 요소이며, 효율을 개선하기 위해 서로 다른 반도체 산화물을 혼합하여 Pastes를 제조해 사용하는 연구가 이루어지고 있다. 본 연구에서는 $TiO_2-Nb_2O_5$ 혼합 반도체 산화물을 제조하여 염료 감응 태양전지의 특성을 분석하였다. 혼합 반도체 산화물이 광 전환 효율에 미치는 전기적인 특성을 분석하기 위해서 $Nb_2O_5$을 서로 다른 비율로 첨가하여 태양전지를 제작하였다. 이에 $Nb_2O_5$가 첨가됨에 따라 전해질과의 접촉에 의한 재결합 현상보다 전도성이 겅화되어 태양전지의 단락 전류, 개방전압, 변환 효율 등이 개선되는 것을 확인하였다.

• 한국재료학회지
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• 제29권9호
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• pp.559-566
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• 2019

$Lu(Nb,Ta)O_4:Eu^{3+}$ powders are synthesized by a solid-state reaction process using LiCl and $Li_2SO_4$ fluxes. The photoluminescence (PL) excitation spectra of the synthesized powders consist of broad bands at approximately 270 nm and sharp peaks in the near ultraviolet region, which are assigned to the $Nb^{5+}-O^{2-}$ charge transfer of $[NbO_4]^{3-}$ niobates and the f-f transition of $Eu^{3+}$, respectively. The PL emission spectra exhibit red peaks assigned to the $^5D_0{\rightarrow}^7F_J$ transitions of $Eu^{3+}$. The strongest peak is obtained at 614 nm ($^5D_0{\rightarrow}^7F_2$), indicating that the $Eu^{3+}$ ions are incorporated into the $Lu^{3+}$ asymmetric sites. The addition of fluxes causes the increase in emission intensity, and $Li_2SO_4$ flux is more effective for enhancement in emission intensity than is LiCl flux. The substitution of $Ta^{5+}$ for $Nb^{5+}$ results in an increase or decrease in the emission intensity of $LuNb_{1-x}Ta_xO_4:Eu^{3+}$ powders, depending on amount and kind of flux. The findings are explained using particle morphology, modification of the $[NbO_4]^{3-}$ structure, formation of substructure of $LuTaO_4$, and change in the crystal field surrounding the $Eu^{3+}$ ions.

• 한국세라믹학회지
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• 제32권9호
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• pp.1056-1064
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• 1995

95Pb(Mg1/3Nb2/3)O3-5PbTiO3 (hereinafter designated as 95PMN-5PT) system was prepared by the columbite-precursor method with 2 mol% excess PbO to compensate the PbO loss during thermal process. The amount of CuO was 1~10 mol%, and the effects of CuO addition on the dielectric properties of this system have been investigated. From the microstructures, XRD analysis and dielectric measurements, the solubility limit of CuO in 95PMN-5PT was found to be around 3 mol%. Lattice parameter and Curie temperature were found to be decreased as the amount of CuO increased up to the solubility limit. This result confirmed that the Cu2+-ions substituted the Pb2+-ions. It was revealed that the addition of CuO on 95PMN-5PT promoted the sinterability and properties. The room temperature dielectric constant, the loss factor and the specific resistivity of the specimens processed with optimum conditions were 23000, 1%, and 8$\times$1011Ω.cm, respectively.

• 한국전기전자재료학회논문지
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• 제27권10호
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• pp.630-634
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• 2014

$(Na_{0.525}K_{0.4425}Li_{0.0375})(Nb_{0.9975}Sb_{0.065}Ta_{0.0375})O_3+0.3 wt%CoO$ ceramics were fabricated as a function of CuO addition by traditional solid state sintering process in order to develop excellent lead-free piezoelectric ceramics composition. The addition of CuO in the LNKNTS composition ceramics can effectively enhance the densification of the ceramics, resulting in the oxygen vacancies as hardening effect. The excellent piezoelectric properties of electromechanical coupling factor($k{\small}_P$) of 0.378, piezoelectric constant($d_{33}$) of 152 pC/N were obtained from the 1.0 mol% CuO doped LNKNTS ceramics sintered at $1,020^{\circ}C$ for 3 h.

• 한국전기전자재료학회논문지
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• 제11권5호
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• pp.378-383
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• 1998

Microstructure and additive effect of Lead Zirconate-Titanate(PZT) ceramics prepared by molten salt synthesis method with additives $Nb_2O_5, Fe_2O_3$ and MnO were investigated.The grain PZT ceramics ws decreased with the increase $Nb^{5+} or Fe^{3+}$ while increased with the increase $Mn^{2+}$ addition. The relative resistivity of PZT ceramics was increased with the increase $Mn^{5+}$ addition, while decreased with the increase $Mn^{2+}$ addition. And the dielectric and the piezoelectric constant of PZT ceramics showed 2,100 and 342pC/N at $Mn^{5+}$ addition of 0.75 mol%, respectively.

• 한국세라믹학회지
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• 제24권3호
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• pp.263-269
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• 1987

It is investigated that the determination of the correlation between the change of microstructure and electrical properties. Yttria is added to the compositiojn of rhombohedral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system. Average grian size, lattice parameters and distribution of yttrium are characterized by XRD, SEM and EDS. Electrical properties are determined by measurement of Curie temperature, piezoelectric properties and hysteresis loops. The results are as follows; 1. Both lattice parameters, a and ${\alpha}$, are changed by addition of yttria to the composition of rhomboheadral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system and Curie temperature is proportional to the values at (90-${\alpha}$).

• 한국분말재료학회지
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• 제9권3호
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• pp.148-152
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• 2002

The microstructures and indentation fracture of pressureless-sintered $DyNbO_4$ crystalline were investigated as a basic study for the application of weak phase of fibrous monolithic composites. They were comprised with many lamella twins as well as micro-cracks at the grain boundaries. The hardness at room temperature was remarkably low value(575 Hv) due to the low relative density and existence of microcracks at grain boundaries. The main fracture mode was a typical intergranular fracture, and showed remarkable micro-cracking effect. The heavy plastic deformation was observed around the site of indentation. In addition, the $DyNbO_4$ was expected to apply as a weak phase in the fibrous monolithic composites because of the low hardness and easily plastic deformation that could be led the preferable pulled-out and microcracking toughening under the failure.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.632-635
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• 2003

[ $(Ba,Sr,Ca)TiO_3$ ] powders, prepared by the sol-gel method, were mixed with organic vehicle and the BSCT thick films were fabricated by the screen printing techniques on alumina substrates. The dielectric properties were investigated for various composition ratio and $Nb_2O_5$ doping contents. All the BSCT thick films, sintered at $1420^{\circ}C$, showed the typical XRD patterns of a perovskite polycrystalline structure. The Curie temperature and the relative dielectric constant decreased with increasing Ca content and $Nb_2O_5$ doping amount. The relative dielectric constant, dielectric loss and tunability of the BSCT(50/40/10) thick films doped with 1.0wt% $Nb_2O_5$ were 1410, 0.65% and 17.29% respectively.