• Electrical & Electronic Materials
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• v.10 no.10
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• pp.1041-1047
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• 1997

In this paper the dielectric properties of (0.8-x)Pb(Mb$_{1}$3//Nb/2/3)O$_3$/BaTiO$_3$-CaZrO$_3$(x=0.1, 0.15, 0.2, 0.25) ceramics were investigated. Specimens were prepared by the conventional mixed oxide method and sintering temperature and time were 1000~115$0^{\circ}C$ 2hr, respectively. The structural and dielectric properties with variation of sintering temperature and composition were investigated. All the specimens sintered at 115$0^{\circ}C$ for 2hr showed the highest value of 1043. With increasing the contents of CZ and frequency dielectric constant was decreased and which was decreased with increasing temperature from 3$0^{\circ}C$ to 15$0^{\circ}C$.

• Transactions on Electrical and Electronic Materials
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• v.8 no.4
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• pp.149-152
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• 2007

[ $(Ba_{0.6}Sr_{0.3}Ca_{0.1})TiO_3$ ](BSCT) thick films doped with 0.1 mol% $MnCO_3\;and\;Yb_2O_3(0.1{\sim}0.7mol%)$ were fabricated by the screen printing method on the alumina substrates. And the structural and electrical properties as a function of $Yb_2O_3$ amount were investigated. The exothermic peak was observed at around $680^{\circ}C$ due to the formation of the poly crystalline perovskite phase. The lattice constants of the BSCT thick film doped with 0.7 mol% is 0.3994 nm. The specimen doped with 0.7 mol% $Yb_2O_3$ showed dense and uniform grains with diameters of about $4.2{\mu}m$. The average thickness of all BSCT thick films was approximately $70{\mu}m$. Relative dielectric constant and dielectric loss of the specimen doped with 0.7 mol% $Yb_2O_3$ were 2823 and 3.4%, respectively. The Curie temperature of the BSCT thick films doped with 0.1 mol% $Yb_2O_3$ was $46^{\circ}C$.

• Electrical & Electronic Materials
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• v.10 no.6
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• pp.533-540
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• 1997

The microwave dielectric properties of ((P $b_{1-x}$ C $a_{x}$)Zr $O_3$ and (P $b_{0.63}$,C $a_{0.37-x}$ $M_{x}$)Zr $O_3$(M=Mg,Sr) ceramics were investigated. In (P $b_{1-x}$ C $a_{x}$)Zr $O_3$ (X=0.33~0.40) ceramics, high quality factor and small temperature coefficient of resonant frequency were obtain in (P $b_{0.63}$C $a_{0.37}$)Zr $O_3$with perovskite structure. In the case of (P $b_{0.63}$C $a_{0.37-x}$M $g_{x}$)Zr $O_3$ dielectric constant temperature coefficient of resonant frequency increased and quality factor decreased due to increase of polarization of A-O bonding. When replacing Ca ion with Sr ion with large ion radius, polarization decreased with increased of bonding length and thus dielectric constant and temperature coefficient of resonant frequency decreased.decreased.creased.

• Journal of the Korean Ceramic Society
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• v.44 no.5 s.300
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• pp.148-150
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• 2007

A process to synthesize $La_{0.8}Sr_{0.2}CrO_3$ (LSC), which is a promising material for use as a separator in a soild oxide fuel cell, is investigated in this study. LSC powders without secondary Phases could be synthesized with ultrasonic spray pyrolysis and a heat treatment at $1200^{\circ}C$ for 20 h; however, it showed an average diameter of $0.6{\mu}m$ with a wide particle size distribution. On the other hand, LSC powders synthesized with spray pyrolysis at $800^{\circ}C$, heat-treated at $900^{\circ}C$ for 5 h, ball-milled and finally heat-treated again at $1200^{\circ}C$ for 20 h showed a smaller average diameter of $0.3{\mu}m$ and narrower size distribution. Very few particles above $0.5{\mu}m$ were found. Thus, a proper combination of the heat treatment and milling process after spray pyrolysis it determined to be very important in synthesizing fine and uniform LSC perovskite powders.

• Journal of the Korean Ceramic Society
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• v.52 no.5
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• pp.308-314
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• 2015

The electrochemical performance and Cr poisoning behavior of $La_{1-x}Ba_xCo_{0.9}Fe_{0.1}O_{3-{\delta}}$ (LBCF, x = 0.3, 0.4, 0.5) and $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ (LSCF) cathodes were investigated for solid oxide fuel cells (SOFCs). The polarization resistance of the LBCF/GDC/LBCF symmetrical cell was found to decrease with increasing Ba content (x value). This phenomenon might be associated with the high oxygen vacancy concentration in the LBCF sample, with x = 0.5. In addition, there was no chromium poisoning in the LBCF cathode. On the other hand, the polarization resistance of the LSCF cathode was found to significantly increase after exposure to gaseous chromium species; it appears that this result stemmed from the formation of $SrCrO_4$ phase. Therefore, it can be expected that LBCF can be a durable potential cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFC).

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1716-1724
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• 2018

Single crystal of organic lead halide ($CH_3NH_3PbX_3$; $CH_3NH^+_3$ = methylammonium (MA), $X=Cl^-$, $Br^-$, $I^-$) is the best candidate for material intrinsic property studies due to no grain boundary and high crystal quality than the film having a lot of grain boundary and surface defects. The representative crystallization methods are inverse temperature crystallization (ITC) and anti-solvent vapor assisted crystallization (AVC). Herein, we report bandgap modulated organic lead halide single crystals having a bandgap ranging from ~ 2.1 eV to ~ 3 eV with ITC and AVC methods. The bandgap modulation was achieved by controlling the solvents and chloride-to-bromide ratio. Structural, optical and compositional properties of prepared crystals were characterized. The results show that the crystals synthesized by the two crystallization methods have similar properties, but the halide ratios in the crystals synthesized by the AVC method are controlled more quantitatively than the crystals synthesized by ITC.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.06a
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• pp.57-60
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• 1998

Lean zirconate titanate (PZT) is an attractive material for the memory device applications. We have investigated Pt and{{{{ { RuO}_{2 } }}}} as a botton electrode for a device application of PZT thin film. The bottom electrodes were prepared by using an RF magnetron sputtering method. The substrate temperature influenced the resistivity of Pt and {{{{ { RuO}_{2 } }}}} a s well as the film crystal structure. XRD examination shows that a preferred(111) orientations for the substrate temperature of 30$0^{\circ}C$. From the XRD and AFM results, we recommend the substrate temperature of 30$0^{\circ}C$ for the bottom electrode growth. We investigated and anneal temperature effect because Perovskite PZT structure is recommended for the memory device applications and the structural transformation is occurred only after and elevated heat treatment. As post anneal temperature was increased from RT to $700^{\circ}C$, the resistivity of Rt and {{{{ { RuO}_{2 } }}}} w as decreased. Surface morphology was observed by AFM as a function of post anneal temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.84-84
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• 2009

$BaTiO_3$는 perovskite 구조를 가지는 대표적인 강유전체 재료로서 MLCC (Multi Layer Ceramic Capacitor), PTC thermistor등에 널리 사용되어지고 있다. 최근 고용량 MLCC의 상업화와 함께 나노크기를 갖는 tetragonal phase의 $BaTiO_3$ 입자를 합성하기 위한 다양한 제조방법이 제시되고 있다. 또한 유전특성과 온도특성 및 신뢰성을 향상시키기 위해 많은 첨가제들이 연구되어지고 있다. 따라서 본 연구에서는 희토류 원소인 $Y_2O_3$를 첨가하여 유전특성 및 온도특성을 향상시키고자 하였다. 본 실험에서는 150nm 크기를 갖는 pure $BaTiO_3$ 분말을 사용하고 $Y_2O_3$의 양은 0.02 ~ 0.1wt%로 변수를 주어 첨가하였으며, 최적의 소결 조건을 찾기 위하여 1200, 1230, $1250^{\circ}C$에서 소결을 진행하였다. 실험방법으로는 균일한 혼합을 위하여 Iso-alcohol을 이용하여 48시간 ball-mill 하였으며 오븐에서 건조 후 ${\Phi}15$로 성형하여 소결을 진행하였다. 실험결과로는 $Y_2O_3$ 첨가량이 0.02wt% 부터 상온부터 상전이 온도 부근의 유전율 기울기는 완만해 지는 것을 확인할 수 있었으며, 소결시편의 정방정비 (tetragonality)도 뚜렷하게 나타났다. $Y_2O_3$ 첨가랑이 0.1 wt% 일 때는 첨가량의 증가로 인해 강유전성이 상쇄됨을 나타냈다. 이는 $2450^{\circ}C$에 이르는 매우 높은 용융온도와 $2350^{\circ}C$까지 상전이가 는 $Y_2O_3$를 미량 첨가할 때, 고온에서 높은 화학적 안정성과 내열성을 가져 온도 안정성이 향상된 것으로 판단된다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.172-172
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• 2009

$BaTiO_3$는 perovskite 구조를 가지는 대표적인 강유전체 재료로서 MLCC(Multi Layer Ceramic Capacitor), PTC thermistor등에 널리 사용되어지고 있다. 최근 고용량 MLCC 의 상업화와 함께 나노크기를 갖는 tetragonal phase의 $BaTiO_3$ 입자를 합성하기 위한 다양한 제조방법이 제시되고 있다. 또한 유전 특성과 온도특성 및 신뢰성을 향상시키기 위해 많은 첨가제들이 연구되어지고 있다. 따라서 이 번 연구에서는 선행 연구를 통해 얻어진 high energy mill을 이용한 고상반응법으로 제조된 $BaTiO_3$를 사용하였으며, 제조된 $BaTiO_3$ 분말에 glass frit를 첨가하여 소결온도 및 유전특성의 변화를 관찰하였다. 제조된 $BaTiO_3$ 분말은 200nm이하의 구형화와 균일한 입자크기를 보였으며, 선행연구를 통해 최적화된 glass frit의 양인 2.53wt%를 첨가하였고 1170, 1200, $1230^{\circ}C$에서 소결하여 소결온도에 따른 변화를 관찰하였다. 실험방법으로는 원료를 혼합하기 위하여 24시간 ball-mill을 이용하여 혼합하였으며, $\Phi15$로 성형하여 소결을 진행하였다. 실험진행 결과 모든 시편에서의 비유전율은 glass frit가 첨가되지 않은 조성보다 높게 나타났으며, $1200^{\circ}C$에서 소결한 시편의 비유전율($\varepsilon_r$)은 2300으로 glass frit가 첨가되지 않은 조성과 비교하여 21% 증가하여 최대치를 나타냈다. 또한 소결온도 $1200^{\circ}C$ 이상에서의 모든 시편에서는 95% 이상의 상대밀도를 나타내어, glass frit가 소결조제로써의 역할을 하는 것으로 나타났다. 따라서 본 연구를 통해 glass frit첨가로 인한 소결온도 감소 및 유전특성이 증가하는 것을 확인 하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.6
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• pp.372-376
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• 2014

We investigated the effect of excess CuO on the sintering behavior, ferroelectric, and piezoelectric properties of lead-free $Bi_{0.5}(Na_{0.82}K_{0.18})_{0.5}TiO_3$ (BNKT) ceramics. The addition of excess CuO was found to greatly contribute to the densification and grain growth, however, excess CuO over 3 mol% was precipitated at grain boundaries after sintering. BNKT with 1~2 mol% CuO in excess sintered at $975^{\circ}C$ showed piezoelectric properties comparable to those of unmodified BNKT sintered at $1,175^{\circ}C$. These results seem meaningful for its application to low cost multilayer actuators (MLAs) because low firing ceramics make it possible to apply less expensive base metals to the inner electrode of MLAs.