• Journal of the Mineralogical Society of Korea
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• v.1 no.2
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• pp.94-103
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• 1988

Diamond anvil cell (DAC) interfaced with a YAG laser heating system has been used to study the phase transformations on perovskite structured titanates ($BaTiO_3$, and $PbTiO_3$) and to synthesize the silicate perovskite phase from the orthopyroxenes of $MgSiO_3$ and $(Mg_{0.87},\;Fe_{0.13})SiO_3$. $BaTiO_3$ and $PbTiO_3$ transform from tetragonal phase to cubic at the pressures of approximately 2.6 GPa and 4.0 GPa at room temperature, respectively. Cubic phases of the both show wide range of stability in the extended in-situ high pressures and high temperature regions. Starting orthoenstatite of $MgSiO_3$ has yielded the perovskite phase as the major structure with ilmenite, gamma-spinel, betta-spinel and stishovite phases at ~38 GPa and ${\sim}1,000^{\circ}C$. $(Mg_{0.87},\;Fe_{0.13})SiO_3$ has shown the perovskite as the major phase with betta-spinel, stishovite and enstatite phases at ~35 GPa and ${\sim}1,000^{\circ}C$. The ilmenite phase does not occur at this condition.

• 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.

• Journal of the Korean Ceramic Society
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• v.28 no.6
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• pp.451-456
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• 1991

Electrical properties of 0.15 mol% Y2O3 doped semiconducting BaTiO3 ceramics have been investigated as functions of Pb5Ge3O11 contents (from 0.25 mol% to 2.5 mol%) and sintering temperatures (from 1150$^{\circ}C$ to 1300$^{\circ}C$). The low-temperature sintered BaTiO3 ceramics above 1150$^{\circ}C$ show increase of Curie temperature due to the diffusion of Pb+2 ions, and their PTCR effects decrease. As the sintering temperature increases the room temperature resistance decreases due to the growth of the grain, but the room temperature resistance increases with the increase of the Pb5Ge3O11 contents by the formation of thick insulating layers at the grain boundary.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.1
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• pp.57-63
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• 2003

The effects of glass addition on the low-temperature sintering and microwave dielectric properties of $BaO-Nd_2O_3-TiO_2$ dielectric ceramics were studied. When 10∼13 wt% of lithium borosilicate glass was added, the sintering temperature decreased from 130$0^{\circ}C$to 850-$900^{\circ}C$relative density of more than 97% was obtained. When the sample was sintered at $850^{\circ}C$ with 10 wt% of glass, the dielectric properties of $\epsilon_r{\ge}54$, $Q{\times}f_0{\ge}2300$, and $\tau_f{\ge}+8ppm/^{\circ}C$ were obtained.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.288-288
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• 2007

본 연구에서 내환원성 $BaTiO_3$의 PTCR(Positive Temperation Coefficient Resistance) 특성 및 미세구조에 대한 분쇄 및 출발 원료들의 하소 조건의 영향을 연구하였다. $BaCO_3$, $TiO_2$, $CeO_2$를 Attrition milling 하여 1차 혼합 및 분쇄한 후 건조하여 혼합분말을 얻었으며, $(Ba_{1-x}Ce_x)TiO_3$를 합성하기 위하여 $1000^{\circ}C{\sim}1200^{\circ}C$ 공기중에서 하소하였다. 각 하소온도에서 제조한 $(Ba_{1-x}Ce_x)TiO_3$에 첨가제를 2차 혼합하고 초미분쇄하여 분말을 제조하였다. 직경 5mm 의 시편을 제조하여 환원 및 재산화 분위기에서 소결을 한 후 상온저항값 및 R-T특성을 측정하였고 SEM 을 통해 미세구조를 관찰하였다. 또한 하소 후 온도에 따른 상분석을 XRD를 통하여 분석하였다. 그 결과 하소온도가 증가함에 따라 상온저항값은 감소하는 경황을 보였으며 PTC특성은 감소하다가 증가하는 경향을 보였다. 초미분쇄에 따른 입자크기는 $1{\mu}m$이하로 작아졌으며 미립화가 됨에 따라 하소/소결온도에 앙향을 줄 것으로 사료된다.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2005.09a
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• pp.175-177
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• 2005

본 연구에서는 fresnoite ($Ba_{2}TiSi_{2}O_{8}$) 결정화 유리를 $xK_{2}O-(33.3-x)BaO-16.7TiO_{2}-50SiO_{2}$ ($0{\le}x{\le}\;20mol\%$)으로 부터 제조하였으며, 특성평가를 하였다. $K_{2}O$의 치환량이 증가함에 따라, 유리전이 온도와 결정화 온도는 감소하였으며, 유리의 안정화를 나타내는 ${\Delta}$T는 증가하였다. $Ba_{2}TiSi_{2}O_{8}$ 결정상의 형성은 XRD와 SEM분석을 통하여 관찰하였고, LCR meter를 사용하여 열처리에 의하여 제조된 결정화 유리의 유전율은 측정하였으며, 결정화 유리는 $Ba_{2}Si_{2}TiO_{8}$ 단결정 보다 낮은 유전율은 보였다.

• Transactions on Electrical and Electronic Materials
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• v.16 no.4
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• pp.179-182
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• 2015

The particle sizes of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ powder were controlled by secondary milling time after calcination. The average particle sizes, Dmean, of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ powders were critically changed from 14.31 μm to 0.91 μm by secondary milling time. The dielectric and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ ceramics depended on the particle sizes of powders after calcination and the secondary milling process. As secondary milling times after calcination were increased to more than 48 hr, the dielectric and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ ceramics were deteriorated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.11
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• pp.947-953
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• 1998

The microwave dielectric properties of X BaO-0.15($Nd_{0.87}Bi_{0.13})_2O_3-(0.85-X)TiO_2 (X=0.14~0.17) and 0.16BaO-0.15(Bi_xNd_{1-x})_2O_3-0.69TiO_2$ (X=0.12~0.15) ceramics sintered at 1320~$1380^{\circ}C$ were investigated. The microwave dielectric properties of X BaO-0.15(Nd_{0.87}Bi_{0.13})_2O_3-(0.85-X)TiO_2$ (X=0.14~0.17) can be controlled effectively by adjusting X content : with increasing X from 0.14 to 0.17 both dielectric constant and temperature coefficient of resonant frequency decreased from 94.6 to 86 and from 22 ppm/^${\circ}C to -7 ppm/^{\circ}C$, respectively, while quality factor increased from 1300 to 1920 (at 4GHz). The microwave dielectric properties of 0.16BaO-0.15(Bi_x/Nd_{1-x2}O_3 -0.69TiO_2$ (X=0.12~0.15) can be controlled effectively by adjusting X content : with increasing X from 0.12 to 0.15 both quality factor and temperature coefficient of resonant frequency decreased from 1920 to 1430 and from 9 ppm/^${\circ}C to -10 ppm/^{\circ}C$, respectively, while dielectric constant increased from 87.5 to 92.6.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.546-552
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• 1993

본 연구에서는 입계의 성질을 이용한 PTCR 재료에 입계 modifier로서 $Bi_{2}$$O_{3}$와 BN을 첨가하고 입계의 미세구조와 결함농도를 변화시켜 이에 따른 소결 및 전기적 특성변화를 TMA, XRD, 복합 임피던스방법 등을 이용하여 해석하였다. 실험 결과 Y이 도우핑된 BaT$iO_{3}$ PTCR 재료에 $Bi_{2}$$O_{3}$를 첨가하였을때 약 0.1mol%까지 고용이 되는 것으로 밝혀졌다. $Bi_{2}$$O_{3}$를 고용한계 이하로 첨가시에는 생성되는 vacancy등의 결함으로 말미암아 Y-BaT$iO_{3}$의 치밀화가 촉진되었으나, 그 이상 첨가하면 치밀화 뿐만 아니라 결정립 성장도 억제되었다.$Bi_{2}$$O_{3}$ 결정립 내부에 Ba와 Ti vacancy가 동시에 생길 수 있어 고온저항이 높아짐을 알 수 있었다. BN은 BaT$iO_{3}$에 고용이 되지 않는 것으로 밝혀졌으며 $B_{2}$O/wub/3를 주성분으로한 액상형성으로 인하여 저온에서의 급격한 치밀화가 관찰되었다. 또 Ba-Y-Ti-B-O의 비정질 상이 tripie junction에 존재함으로서 상온저항이 크게 변화하였으며, PTCR jump도 높아졌다.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.741-746
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• 1990

Dielectrics which do not lose their high insulation resistance in reducing atmosphere are necessary for multilayer ceramic capacitors with Ni internal electrode. In this study we investigated the Ca ion site occupancy in A-site excess Ca-doped BaTiO3 by measuring the insulation resistance, lattice constant and Curie temperature. Its Curie temperature, which was lower than that of the pure BaTiO3, was more lowered by sintering in reducing atmosphere. Lattice constnat of c-axis decreased and that of a-axis increased, suggesting substitution of Ca ions for Ti ions. Hence CaTi" acts as an acceptor to maintain high insulation resistance.ance.