• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.9
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• pp.702-710
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• 2012

Eco-friendly $(Na,K)NbO_3$ (NKN)-based piezoelectric ceramic materials were fabricated by conventional ceramic method for shear mode piezoelectric energy harvesting application. $NKN-LiTaO_3$ (LT) based compositions were adopted for the high $d_{15}{\times}g_{15}$ which is proportional to harvested energy density. The composition $0.935(Na_{0.535}K_{0.485})NbO_3-0.065LiTaO_3$ was found to be lie on the boundary of tetragonal and orthorhombic phases. With reducing Ta content, the dielectric constant decreased gradually while maintaining high $d_{15}$, which resulted in increased $d_{15}{\times}g_{15}$. The composition $0.935(Na_{0.535}K_{0.485})NbO_3-0.065Li(Nb_{0.990}Ta_{0.010})O_3$ was found to possess excellent piezoelectric and electromechanical properties ($d_{15}{\times}g_{15}=29\;pm^2/N$, $d_{15}$ = 417 pC/N, $k_{15}$ = 0.55), and high curie temperature ($T_c=455^{\circ}C$).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.210-211
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• 2005

[ $(K_{0.5}Na_{0.5})NbO_3$ ](KNN) 세라믹스의 소결 특성과 압전 특성을 높이기 위해 B-site에 Sb를 치환하여 Sb함량에 따른 특성을 측정 하였다. Sb 의 함량을 0mol $\sim$ 0.1mol 까지 첨가한 결과 소결 밀도는 Sb의 첨가량이 많아질수록 증가하다 Sb-0.08mol에서 4.40g/$cm^3$으로 가장 높은 밀도를 가졌으며, 여기서의 전기기계 결합 계수가(Kp) 0.45로 높은 값을 나타내었다. 상전 이 온도는 375$^{\circ}C$로 순수한 KNN 의 420$^{\circ}C$ 보다 약 45$^{\circ}C$정도 떨어졌으나 orthorhombic에 서 tetragonal 로 바뀌는 전이 온도는 KNN이 220$^{\circ}C$, KNNS 가 225$^{\circ}C$로 크게 변하지 않았다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.327-327
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• 2008

Lead-free $(K_{0.5}Na_{0.5})NbO_3$ 압전 세라믹스는 다양한 광소자로의 응용과 압전 특성, 초전 특성을 이용한 압전 소자로의 응용이 가능한 재료로 보고되고 있다. 그러나 KNN계 압전소재 특성상 판상 형태의 결정립으로 인해 낮은 소결 밀도를 갖게 되고, 그로인해 압전물성의 저하를 초래하는 문제점을 가지고 있다. 따라서, 본연구에서는 다양한 밀링 방법을 적용하여 입자 사이즈를 작게 하고 소성체의 결정립을 구형화 함으로써 저온소결에서의 압전물성을 개선시키고자 한다. $(K_{0.5}Na_{0.5})NbO_3$를 기계적 분쇄법에 의해 입자사이즈에 따라 변화되는 상의 분석과 압전체로서의 특성을 관찰하였다. 결정학적 상분석 및 미세 조직은 XRD, SEM을 이용하여 관찰하였고, Capacitance는 Impedance analyzer(HP4192A)로 측정하였으며, Impedance 주파수 특성은 Network Analyzer로 측정하여 Kp, Kt와 Qm을 측정하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.59-59
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• 2008

Pb(Zr,Ti)$O_3$(PZT)는 현재 가장 우수한 압전특성을 가진 압전 재료로써, 압전효과와 역압전효과를 이용한 압전 액추에이터, 압전 트랜스듀서, 센서, 레조네이터 등의 활동에 대한 연구과 활발하게 이루어 지고 있다. 그러나 압전성이 우수한 PZT 세라믹스들은 Pb 성분이 포함되어 있기 때문에 환경오염뿐 아니라, 경제적인 측면에서도 많은 문제점을 가지고 있어 최근에는 유해원소인 Pb를 포함하지 않는 친환경 압전 세라믹스에 관한 연구가 활발히 진행되고 있다. (Na, K)$NbO_3$은 뛰어난 특성을 가지고 있어 Pb를 기본조성으로 하는 압전세라믹스를 대체할 수 있는 대표적인 물질중의 하나로 알려져 있다. 그러나, potassium의 수분과의 반응성과, 소결시 휘발로 인해 높은 소결밀도의 NKN을 제조하기 어렵다. 이러한 단점을 보안하기 위해 Hot pressing, Hot forging, SPS 등 여러가지 방법을 이용하여 연구가 수행되고 있지만, 고가의 제조공정을 이용해야만 한다. 본 연구에서는 $BaSrTiO_3$의 새로운 고용체를 추가시켜 기본 NKN 조성보다 소결밀도, 유전 및 압전특성을 향상시키고자 하였다.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.73-78
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• 2019

Lead free $(Ba_{0.7}Ca_{0.3})TiO_3$ thick films with nano-sized grains are prepared using an aerosol deposition (AD) method at room temperature. The crystallinity of the AD thick films is enhanced by a post annealing process. Contrary to the sharp phase transition of bulk ceramics that has been reported, AD films show broad phase transition behaviors due to the nano-sized grains. The polarization-electric hysteresis loop of annealed AD film shows ferroelectric behaviors. With an increase in annealing temperature, the saturation polarization increases because of an increase in crystallinity. However, the remnant polarization and cohesive field are not affected by the annealing temperature. BCT AD thick films annealed at $700^{\circ}C/2h$ have an energy density of $1.84J/cm^3$ and a charge-discharge efficiency of 69.9 %, which is much higher than those of bulk ceramic with the same composition. The higher energy storage properties are likely due to the increase in the breakdown field from a large number of grain boundaries of nano-sized grains.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.14-17
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• 2014

In this study, lead-free Piezoelectric $(Na_{0.47}K_{0.47}Sr_{0.03}Ca_{0.03})(Nb_{0.94}Ti_{0.06})O_3$-0.1 $MnO_2$ ceramics were fabricated using mixed oxide method and the effects of various sintering temperature on the structural and electrical properties were investigated. For the $(Na_{0.47}K_{0.47}Sr_{0.03}Ca_{0.03})(Nb_{0.94}Ti_{0.06})O_3$-0.1 $MnO_2$ (NKN-SCT-$MnO_2$) ceramics sintered at temperatures of $1,025{\sim}1,100^{\circ}C$. The results indicated that all specimens were perovskite single phase formation without any second phase. It has been shown that relative density is increased to increasing sintering temperature. When the sintered temperature at $1,075^{\circ}C$, highest sintered density and maximum value of $4.45g/cm^3$. Average grain size is increased to increasing sintering temperature. The electromechanical coupling factor, dielectric constant, dielectric loss, d33 and curie temperature at the sintering temperature $1,075^{\circ}C$ of NKN-SCT-$MnO_2$ specimens were 0.22, 511, 0.033, 103 and $380^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.35-40
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• 2009

Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ solid solution were prepared by a conventional solid state reaction method. The phase structure was showed single phase with perovskite structure regardless calcinations temperature and $Ba_{1-x}(Bi_{0.5}Na_{0.5})_xTiO_3$ structure was transformed from tetragonal to orthorhombic phase at $x{\geq}0.15$ mole. The XRD peaks with $45^{\circ}{\sim}46^{\circ}$ shifted in right the influence of crystal structure change and the intensity of peak was decreased with additive $(Bi_{0.5}Na_{0.5})TiO_3$. The curie temperature risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but disappeared for $(Bi_{0.5}Na_{0.5})TiO_3$ addition more than 0.15 mole in TMA. In relative permittivity, the curie temperature by the transform of ferroelectric phase risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but decreased in relative permittivity. Also, the peak of new curie temperature showed the sample containing $0.025{\sim}0.045$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ near $70^{\circ}C$ caused by phase transform from ferroelectric to ferroelectric and the peak of new curie temperature disappeared at 0.045 mole of $(Bi_{0.5}Na_{0.5})TiO_3$. In our study, it was found that the PTCR in $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ system was possible for $0{\sim}0.025$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ and the maximum curie temperature by phase transition showed about at $145^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.52-52
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• 2008

The positive temperature coefficient of resistivity (PTCR) effect in (1-x)$BaTiO_3$ - $x(Bi_{0.5}K_{0.5})TiO_3$ doped with $Nb_2O_5$ was investigated. $(Bi_{1/2}K_{1/2})TiO_3$ (BKT) is more environment-friendly than $PbTiO_3$ in order to use in PTC thermistors. The incorporation of 1 mol% BKT to $BaTiO_3$ increased the Curie temperature (Tc) to $148^{\circ}C$. Doping of $Nb_2O_5$ to $Ba_{0.99}(Bi_{0.5}K_{0.5})_{0.01}TiO_3$ (BaBKT) ceramic has enhanced its PTCR effects. For the sample containing 0.025 mol% $Nb_2O_5$, it showed good PTCR properties; low resistivity at room temperature (${\rho}_r$) of 30 $\Omega{\cdot}cm$, a high PTCR intensity of approximately $3.3\times10^3$, implying the ratio of maximum resistivity to minimum resistivity (${\rho}_{max}/{\rho}_{min}$) in the measured temperature range, and a large resistivity temperature factor (a) of 13.7%/$^{\circ}C$ along with a high Curie temperature (Tc) of $167^{\circ}C$. In addition, the cooling rate of the samples during the sintering process had an influence on their PTCR behavior. All the samples showed the best ${\rho}_{max}/{\rho}_{min}$ ratio when they have cooled down at a rate of $600^{\circ}C$/min.