• 전자공학회논문지 IE
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• v.43 no.2
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• pp.7-10
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• 2006

A GaN-based metal-insulator-semiconductor (MIS) structure has been fabricated by using $BaTa_2O_6$ instead of conventional oxide as insulator gate. The leakage current o) films are in order of $10^{-12}-10^{-13}A/cm^2$ for GaN on $Al_2O_3$(0001) substrate and in order of $10^{-6}-10^{-7}A/cm^2$ for GaN on GaAs(001) substrate. The leakage current of thses films is governed by space-charge-limited current over 45 MV/cm in case of GaN on $Al_2O_3$(0001) substrate and by Poole-Frenkel emission in case of GaN on GaAs(001).

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.448-454
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• 2007

Hydrothermal synthesis was conducted with starting material as Barium hydroxide and hydrous titania ($TiO_2{\cdot}xH_2O$) to obtain barium titanate fine Powder. The conversion, crystal structure and properties of as-prepared powder were investigated according to reaction temperature, time and concentration. The effect of variables on conversion was in order of time < temperature < concentration and the maximum conversion reached to 99.5% in the case of hydrothermal synthesis at $180^{\circ}C$ for 2 h with 2.0 M reactant concentration. At low concentration such as 0.25 M, formation of unreacted $BaCO_3$ and $TiO_2$ was not inevitable at even high reaction temperature and these components converted into $BaTi_2O_5$ at high temperature and remained as impurity. As concentration of reactant increased, the size of as-synthesized $BaTiO_3$ powder deceased and Ba/Ti molar ratio approached into 1, showing Ba/Ti ratio of $1{\pm}0.005$ for reaction at $180^{\circ}C$ for 2 h with 2.0 M concentration.

• Journal of the Korean Ceramic Society
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• v.17 no.1
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• pp.8-12
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• 1980

CaO was added to the $MgAlCrO_4$ spinel, a main component of the mag-chro refractroies, by 0, 1, 5 and 10 mol% before sintering at 135$0^{\circ}C$ in air. The X-ray diffraction analysis produced an additional X-ray diffraction pattern of 8CaO.$6Al_2O_3$.$2CrO_3$ besides that of $MgAlCrO_4$. The formation of 8CaO.$6Al_2O_3$.$2CrO_3$ was interpreted as due to the presence of CaO.8CaO.$6Al_2O_3$.$2CrO_3$ was unstable and easily vaporized. It was concluded that formation of the unstable pollutant 8CaO.$6Al_2O_3$.$2CrO_3$ could be prevented in reducing atmospheres. It was found that the basic refractories containing $Al_2 O_3 -CaO-Cr_2 O_3$ system would be more stable and much less toxic in reducing at mospheres than in oxidizing stmosphere.

• Journal of Electrochemical Science and Technology
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• v.2 no.3
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• pp.146-151
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• 2011

The formation of Li-Si-O phases, $Li_4SiO_4$ and $Li_2SiO_3$ from the starting materials SiO and $Li_2O$ are analyzed using Vienna Ab-initio Simulation (VASP) package and the total energies of Li-Si-O compounds are evaluated using Projector Augmented Wave (PAW) method and correlated the structural characteristics of the binary system SiO-$Li_2O$ with experimental data from electrochemical method. Despite $Li_2SiO_3$ becomes stable phase by virtue of lowest formation energy calculated through VASP, the experimental method shows presence of $Li_4SiO_4$ as the only product formed when SiO and $Li_2O$ reacts during slow heating to reach $550^{\circ}C$ and found no evidence for the formation of $Li_2SiO_3$. Also, higher density of $Li_4SiO_4$(2.42 g $ml^{-1}$) compared to the compositional mixture $1SiO_2-2Li_2O$ (2.226 g $ml^{-1}$) and better cycle capacity observed through experiment proves that $Li_4SiO_4$ as the most stable anode supported by better cycleabilityfor lithium ion battery remains as paradox from the point of view of VASP calculations.

• Korean Journal of Materials Research
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• v.29 no.11
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• pp.690-696
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• 2019

Geopolymer is an alumina silicate-based ceramic material that has good heat-resistance and fire-resistance; it can be cured at room temperature, and thus its manufacturing process is simple. Geopolymer can be used as a reinforcement or floor finish for high-speed curing applications. In this manuscript, we investigate a high-speed curing geopolymer achieved by adding calcium to augment the curing rate. Metakaolin is used as the main raw material, and aqueous solutions of KOH and $K_2SiO_3$ are used as the activators. As a result of optimizing the high bending strength as a target factor for geopolymers with $SiO_2/Al_2O_3$ ratio of 4.1 ~ 4.8, the optimum ranges of the active agent are found to be $0.1{\leq}K_2O/SiO_2{\leq}0.4$ and $10{\leq}H_2O/K_2O{\leq}32.5$, and the optimum range of the curing accelerator is found to be $$0.82{\leq_-}Ca(OH)_2/Al_2O_3{\leq_-}2.87$$. The maximum flexural strength is found to be 1.35 MPa at $Ca(OH)_2/Al_2O_3=2.82$, $K_2O/SiO_2=0.3$, and $H_2O/K_2O=11.3$. The physical and thermal properties are analyzed to validate the applicability of these materials as industrial insulating parts or repairing finishing materials in construction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.330-330
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• 2008

$Fe_2O_3$ added Pb$(Ni_{1/3}Nb_{2/3})O_3-PbTiO_3-PbZrO_3 $ (PNN-PT-PZ) ceramics were produced in order to use them as a bimoph acturator for energy harvesting. Especially, the 0.25 wt% $Fe_2O_3$ added 0.4PNN-0.357PT-0.243PZ, having the composition of morphotropic phase boundary, showed good piezoelectric properties of $d_{33}$ of 810 pC/N, $k_p$ of 77% and $Q_m$ of 55 along with a high Curie temperature of $210^{\circ}C$. A bimorph actuator, composed of the two piezoelectric layers bonded together with a phosphorous bronze layer as a central metallic electrode, was successfully fabricated. The bimorph actuator, vibrated with a 1.3 mm amplitude at 68 Hz, produced high electric power of approximately 60 mW.

• Transactions on Electrical and Electronic Materials
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• v.15 no.3
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• pp.164-169
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• 2014

We investigated the etching characteristics of $HfAlO_3$ thin films in $O_2/Cl_2/Ar$ and $O_2/BCl_3/Ar$ gas, using a high-density plasma (HDP) system. The etch rates of the $HfAlO_3$ thin film obtained were 30.1 nm/min and 36 nm/min in the $O_2/Cl_2/Ar$ (3:4:16 sccm) and $O_2/BCl_3/Ar$ (3:4:16 sccm) gas mixtures, respectively. At the same time, the etch rate was measured as a function of the etching parameter, namely as the process pressure. The chemical states on the surface of the etched $HfAlO_3$ thin films were investigated by X-ray photoelectron spectroscopy. Auger electron spectroscopy was used for elemental analysis on the surface of the etched $HfAlO_3$ thin films. These surface analyses confirm that the surface of the etched $HfAlO_3$ thin film is formed with nonvolatile by-product. Also, Cl-O can protect the sidewall due to additional $O_2$.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.571-576
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• 1988

The microstructure and electrical properties of 0.02Pb[Cd1/2W1/2)O3-0.505PbZrO3-0.475PbTiO3 with MnO2 addition have been investigated. The amount of MnO2 addition was 0, 0.2, 0.4, 0.6, 0.8, 1wt%, respectively. When MnO2 is added up to 0.2wt%, Mn3+ which is substituted for Ti4+ site make hole and act as a acceptor. When MnO2 is added over 0.2wt% Mn3+ which is substituted for Cd2+ site create electron and act as a donor. The variation of grain size show that it was rapidly increased by 0.4wt% addition of MnO2, and while that in the range of over 0.6wt% addition of MnO2 it was decreased. The solid solution range of MnO2 that assumed in this composition according to the variations of microstructure and electrical properties was 0.4-0.6wt%.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.30-35
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• 1999

For dolomite clinkers used as stamp materials, the corrostion behavior of those by slag was inverstigated between 1550$^{\circ}C$ and 1650$^{\circ}C$. Fe2O3 among slag components was selectively penetrated into the grain boundaries of dolomite clinkers. In hot face, the magnesioferrite was preferentially formed by Fe2O3 component contained in dolomite clinker rather than Fe2O3 of slag. The corrosion steps of dolomite clinkers by slag were found as follows ; (1) The dicalciumferrite was formed by the reaction of the calcia within dolomite clinkers with Fe2O3 of slag. (2) The magnesia within dolomite clinkers reacted with the dicalciumferrite to from magnesioferrite and the residual calcia within dolomite clinkers reacted with the dicalciumferrite to form magnesioferrite and the residual calcia was dissolved into slag. (3) The magnesioferrite was corroded by CaO-SiO2 compounds of slag. With the temperature of slag increased, the magnesioferrite layer in hot face was decreased for dolomite clinker without Fe2O3 while the layer thickness and grain sizes of magnesioferrite was increased for dolomite clinker with Fe2O3.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.275-285
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• 1996

The effect of heat-treatment on catalytic crystallization in $LI_2O-Al_2O_3-SiO_2$ glass system over its glass transition temperature was investigated. Glass composition $4Li_2O{cdot}22AL_2O_3{cdot}66SiO_2{cdot}2TiO_2{cdot}2.5ZrO_2{cdot}1.5P_2O_5{cdot}1.0Na_2O{cdot}1.0As_2O_3$ (wt%) was selected and heat-treated at different heating conditions to obtain transparent glass-ceramic. Nucleation and crystallization behaviour of this composition were estimated by differential thermal analysis (DTA) and X-ray diffractometer (XRD) and its thermal expansion coefficients were measured by Dilatometer. As a result, glass transition temperature was $730^{\circ}C$ and two maximum nucleation temperatures were estimated at $730^{\circ}C$ and 82$0^{\circ}C$ using JMA(Johson-Mehl-Avrami) equation by DTA. $ZrTiO_4$ $\beta$-Quartz solid solution and $\beta$-Spodumene crystals were identified by XRD. The optimum crystallization temperature was 92$0^{\circ}C$ and three step heating schedule was expected to be useful to obtain transparent glass-ceramic.