• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.1
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• pp.183-193
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• 1999

Semiconducting (Sr0.85Ca0.15)TiO3 ceramics were prepared by conventional powder synthesis techniques, and then alkaline metallic cations were diffused into the ceramic bodies. The threshold voltage of the ceramics increases with increasing diffusion time and the amount of diffused materials. The ceramics had boundary potential heights of 0.01 ~ 2.89 eV, while their boundary resistance ranged from 2.2 $M{\Omega}$ to 120.4 $M{\Omega}$. Such electrical characteristics of the boundaries were correlated with the boundary structure of the ceramics obtained by transmission electron microscopy.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.553-561
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• 1993

In this study, thr effect of $Bi_2O_3$ and BN addition as grain boundary modifiers on sintering and electrical properties of semiconducting PTCR(Positive Temperature Coefficient of Resistivity) mate rial were analyzed using TMA, XRD and Complex Impedance Spectroscopy method. Bismut.h Ox~de and Boron Nitride were added to Y-doped $BaTiO_3$ respectively. Bismuth sesquioxide up to O.lmol%solubil~ ty limit of $Bi_2O_3$ in Y--$BaTiO_3$ ceramics-retarded densification and grain growth, and further addition mitigated these retardation effects. The resistivity at room temperature increased with increasing amount of $Bi_2O_3$ and thus decreased the PTCR effect, probably due to the $Bi_2O_3$ segregation on the grain boundaries. From the complex ~mpedance pattern, it is known that the grain boundary resisitivity is dominant on the whole resistivity of sample. In the result of applying the defect chemistry, $Bi^{3+} \;and \; Bi^[5+}$ are substituted for Ua and Ti site, respectively. Boron nitride decomposed and formed liquid phase among the $BaTiO_3$ grains. The decomposed com~ ponents made the second phase and existed the tr~ple juntion from the result of EPMA. From the complex impendencc pattern, the gram and grain boundary resistivity were small. The grain size increased with increasing BN contents, and decreased grain boundary resistivity enhanced the PTCR effect.

• 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 Korean Ceramic Society
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• v.38 no.4
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• pp.380-387
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• 2001

140$0^{\circ}C$ 환원 분위기(질소-수소) 조건에서 열처리하여 반도성 SrTiO$_3$하소분말을 제조하였다. 하소분말을 이용하여 135$0^{\circ}C$에서 2시간동안 상압 소결하여 소결체를 제조하였으며, 이때 소결 분위기에 따른 소결체 입계의 전기적 특성을 고찰하였다. 이들 소결체는 전형적인 바리스터 특성을 나타내었으며, 특히 소결 분위기를 질소-수소로부터 공기로 변화시킴에 따라서 소결체의 문턱 전압, 입계 비저항 그리고 입계 전위 장벽은 430V/cm, 10MΩ.cm 그리고 2.0$\times$$10^{-3}$eV로부터 1000V/cm 이상, 240 MΩ.m 그리고 1.1eV로 변하였다.

• Journal of the Korean Ceramic Society
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• v.37 no.12
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• pp.1150-1158
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• 2000

반도성 SrTiO$_3$분말을 이용하여 상압에서 제조된 소결체의 소결 분위기에 따른 소결체 입계의 결함 화학 및 전기적 특성을 고찰하였다. 소결 분위기를 질소-수소, 질소, 공기로 변화시킴에 따라서 입계에서 O/(Sr+Ti)의 비는 1.6로부터 2.1로 증가하였으며, 또한 입계의 과잉 음전하층에서 전하 밀도는 1C/$ extrm{cm}^2$로부터 1.26C/$\textrm{cm}^2$로 증가하였다. 소결체의 문턱 전압, 입계 저항 그리고 입계 전위 장벽은 소결 분위기를 질소-수소로부터 공기로 변화시킴에 따라 6.40-1000 V/cm, 2.70-3050 kΩ 그리고 0.08-10.9 eV로 각각 증가하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.318-322
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• 1997

The (Sr$_{l-x}$.Ca$_{x}$)TiO$_3$(0.05$\leq$x$\leq$0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[$^{\circ}C$] in a reducing atmosphere($N_2$gas). After being fired in a reducing atmosphere, metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100[$^{\circ}C$] for 2 hours and cooled to room temperature. The grain boundary was composed of the continuous insulating layers. The capacitance changes slowly and almost linearly in the temperature region of -30~+85[$^{\circ}C$]. The capacitance characteristics appears a stable value within $\pm$10[%]. The conduction mechanism of the specimens observed in the temperature range of 25~125[$^{\circ}C$], and is divined into three regions haying different mechanism as the current increased: the region I below 230[V/cm] shows the ohmic conduction. The region II can be explained by the Poole-Frenkel emission theory, and the region III is dominated by the tunneling effect.ect.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.12
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• pp.1610-1616
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$(0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere (N$_{2}$ gas). After being fired in a reducing atmosphere, metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100[.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. The results of the capacitance-valtage measurements indicated that the grain boundary was composed of the continuous insulating layers. The capacitance is almost unchanged below about 20[V], but decreased slowly over 20[V]. The conduction mechanism of the specimens observed in the temperature range of 25~125[.deg. C], and is divided into three regions having different mechanism as the current increased: the region I below 200[V/cm] shows the ohmic conduction. The region II between 200[V/cm] and 2000[V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000[V/cm] is dominated by the tunneling effect.ct.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.355-358
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• 1988

Polycrystalline transparent semiconducting zinc oxide film has been characterized for their electrical properties. The conductivity of the film could be increased by approximately five times of magnitude by annealing it in hydrogen at 400 C. The electrical properties measured on the temperature range of RT to 120 K give support well to the model which depicts the importance of the grain boundary effects on the electrical conduction of zinc oxide film.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.137-141
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• 2010

The $(1-x)La_{0.7}Sr_{0.3}MnO_3(LSMO)/xZnFe_2O_4$(ZFO) (x = 0, 0.01, 0.03, 0.06 and 0.09) composites were prepared by a conventional solid-state reaction method. We investigated the structural properties, magnetic properties and electrical transport properties of (1-x)LSMO/xZFO composites using X-ray diffraction (XRD), scanning electron microscopy (SEM), field-cooled dc magnetization and magnetoresistance (MR) measurements. The XRD and SEM results indicate that LSMO and ZFO coexist in the composites and the ZFO mostly segregates at the grain boundaries of LSMO, which agreed well with the results of the magnetic measurements. The resistivity of the samples increased by the increase of the ZFO doping level. A clear metal-to-insulator (M-I) transition was observed at 360K in pure LSMO. The introduction of ZFO further downshifted the transition temperature (350K-160K) while the transition disappeared in the sample (x = 0.09) and it presented insulating/semiconducting behavior in the measured temperature range (100K to 400K). The MR was measured in the presence of the 10kOe field. Compared with pure LSMO, the enhancement of low-field magnetoresistance (LFMR) was observed in the composites. It was clearly observed that the magnetoresistance effect of x = 0.03 was enhanced at room temperature range. These phenomena can be explained using the double-exchange (DE) mechanism, the grain boundary effect and the intrinsic transport properties together.