• Journal of Korea Foundry Society
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• v.33 no.3
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• pp.127-133
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• 2013

The influences of a small amount of CaO addition on the microstructure and corrosion behavior of AZ81 casting alloy have been investigated by means of optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, immersion and electrochemical tests. The added CaO led to the refinement of ${\alpha}$-Mg grains and the decrease in ${\beta}$ precipitate content by the formation of an $Al_2Ca$ phase. The AZ81-CaO alloy had a better corrosion resistance than the AZ81 alloy. The microstructural characterization on the corroded surface revealed that the enhanced corrosion resistance of the CaO-containing alloy may well be ascribed to the increased barrier effect of precipitates formed more continuously along the grain boundaries and the incorporation of Al and Ca elements into the corrosion film, by which it became more protective.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1989.06a
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• pp.101-104
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• 1989

Thermal Electet of the Zinc Oxide varistor has been studied in the temperature range of -130~200[$^{\circ}C$] and the electric field of 6[kV/m]. It appears that there are four peaks of thermally stimulated current; $\alpha$, $\beta$, ${\gamma}$ and $\delta$ spectra appearing at the temperature range of 160, 130, 20 and -30[$^{\circ}C$], respectively. It seems that the origin of $\alpha$, $\beta$, ${\gamma}$ and $\delta$ peaks are associated with the depolarization of donor ions in the depletion layer, the detrapping of trapped electron in the surface, the detrapping of trapped electron in the donor level and the detrapping of trapped electron between grain and intergranular, respectively.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.817-820
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• 1988

Thermal Electet of the Zinc Oxide varistor has been studied in the temperature range of -130${\sim}200[^{\circ}C]$ and the electric field of 6[kV/m]. It appears that there are four peaks of thermally stimulated current; ${\alpha},\;{\beta},\;{\gamma}$ and ${\delta}$ spectra appearing at the temperature range of 160, 130, 20 and $-30[^{\circ}C]$, respectively. It seems that the origins of ${\alpha},\;{\beta},\;{\gamma}$ and ${\delta}$ peaks are associated with the depolarization of donor ions in the depletion layer, the detrapping of trapped electron in the surface, the detrapping of trapped electron in the donor level and the detrapping of trapped electron between grain and intergranular, respectively.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.145-146
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• 2012

Al이 2wt% 첨가된 AZO(Al-doped ZnO) 타겟을 기판을 가열한 대향 타겟 마그네트론 스퍼터링법을 이용하여 수소 유량에 따라 유리기판 위에 AZO 박막을 증착하였다. 수소 유량에 따른 AZO 박막내의 carrier concentration와 mobility의 변화를 확인하였으며 박막내 crystallinity와 grain size의 변화를 확인하였다. 증착된 AZO 박막 특성의 구조적, 전기적, 광학적 변화조사하고 비저항 및 광투과도 등을 분석하여 투명전극용으로 적합한지 연구하였다.

• Bulletin of the Korean Chemical Society
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• v.20 no.9
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• pp.1035-1039
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• 1999

Manganese-activated zincgallate (Zn1-xMnxGa2O4) phosphor as a green phosphor was readily prepared by coprecipitation in aqueous basic solution of metal salts. The obtained product converted to amorphous zincgallate even at 300℃, followed by crystallization at 1000 ℃. The pyrolyzed phosphor showed fine particle, then reduction treatment at 900 ℃ changed into homogeneous shape with slight grain growth(particle size less than 0.5 mm). The photoluminescence characteristics of the zincgallates have been investigated as a function of dopant concentrations, reducing atmospheres and temperatures. Under UV excitation the phosphors displayed the highest green emission efficiency at 504 nm when the specimen oxidized at 1000 ℃ was reduced at 900 ℃ in a mild hydrogen atmosphere (97% N2, 3% H2) with a flow rate of 100 ml/min.

• Journal of the Korean Magnetics Society
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• v.18 no.2
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• pp.58-62
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• 2008

$Ni_{0.4}Zn_{0.4}Cu_{0.2}Fe_2O_4$ ferrite was fabricated by solid stat reaction method and sol-gel method. Because of the drawbacks of each method, we combined these two methods together. We proposed and experimentally verified that nanocrystalline ferrite additive was effective on improving the densification behavior and magnetic properties of NiZnCu ferrites for multilayer chip inductors. The initial permeability of the toroidal core Sample with 20 wt% nanocrystalline ferrite increased from 78.1 to 178.2 as annealing temperature is increased from $880^{\circ}C$ to $920^{\circ}C$. The density, shrinkage and saturation magnetization were increased with increasing annealing temperature, which was attributed to the decrease of additive grain size and increase of sintering density.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1279_1280
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• 2009

Vanadium dioxide(VO2) has been reported to be the most attractive material for thermochromic windows due to its semiconductor-metal phase transition at around $68^{\circ}C$. However, our previous experiment showed it is difficult to grow VO2 thin films directly on glass substrate, whereas thermochromic VO2 thin films were successfully grown on R-cut sapphire substrate. Properties of VO2 thin films on different orientations of sapphire substrates were already reported. Furthermore, VO2 thin films were successfully grown heteroepitaxially on (001) preferred oriented ZnO coated glass. We deposited VO2 thin films using V2O5 targets on substrates with various lattice parameters with same orientation(SrTiO3, MgO, and Sapphire substrate of (001) orientation) by pulsed laser deposition. In this work, we will discuss the effects of lattice misfit, substrate-induced stress and grain size on the properties of VO2 thin films deposited on various substrate materials.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.943-948
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• 2003

The microstructure and electrical characteristics of Zn-Pr-Co-Cr-Dy oxides-based varistors were investigated with Dy$_2$ $O_3$ content in the range of 0.0∼2.0 ㏖%. As Dy$_2$ $O_3$ content is increased, the average grain size was decreased in the range of 18.2∼4.6 $\mu\textrm{m}$ and the ceramic density was decreased in the range of 5.49∼4.64 g/㎤. The incorporation of Dy$_2$ $O_3$ markedly enhanced the nonlinear properties of varistors more than 9 times in nonlinear exponent, compared with the varistor without Dy$_2$ $O_3$ The varistor with 0.5∼1.0 ㏖% Dy$_2$ $O_3$ exhibited the high nonlinearity, in which the nonlinear exponent is above 55 and the leakage current is below 1.0 ${\mu}\textrm{A}$. The donor concentration and the density of interface states were decreased in the range of (4.66∼0.25)${\times}$10$\^$18//㎤ and (5.70∼1.39)${\times}$10$\^$12//$\textrm{cm}^2$, respectively, with increasing Dy$_2$ $O_3$ content. The minimum dielectric dissipation factor of 0.0023 was obtained for 0.5 ㏖% Dy$_2$ $O_3$, but further addition of Dy$_2$ $O_3$ increased it.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.10
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• pp.796-801
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• 2001

Ferroelectric 0.05PZN-xPZT(90/10)-(0.95-x)PZT(10/90) (x=0.65, 0.85) specimens were fabricated by the solid-state reaction method, and especially PZT(90/10) and PZT(10/90) powders were derived by the sol-gel method. All specimens showed a uniform ferroelectric grain without the presence of the pyrocholre phase. Average grain size increased with an increased in sintering temperature, the values for the x=0.65 and x=0.85 specimens sintered at 125$0^{\circ}C$ were 14.4$\mu$m and 9.8$\mu$m, respectively. The dielectric constant and dielectric loss of the x=0.65 specimen sintered at 125$0^{\circ}C$ were 1247. 2.06%, respectively. The coercive field and the remanent polarization of x=0.65 and x=0.85 specimens sintered at 125$0^{\circ}C$ were 8.5kV/cm, 13$\mu$C/$\textrm{cm}^2$ and 17.2kV/cm, 28 $\mu$C/$\textrm{cm}^2$, respectively. The pyroelectric coefficient of the x=0.65 and x=0.85 specimens sintered at 125$0^{\circ}C$ were 5.64$\times$10$^{-8}$ C/$\textrm{cm}^2$K and 2.76$\times$10$^{-8}$ C/$\textrm{cm}^2$K, respectively.