• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.219-223
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• 2005

A promising capacitor, which has conformable step coverage and good uniformity of thickness and composition, is needed to manufacture high-density non-volatile FeRAM capacitors with a stacked cell structure. In this study, ferroelectric $Bi_{3.61}Nd_{0.39}Ti_3O_{12}$ (BNdT) thin films were prepared on $Pt(111)/TiO_2/SiO_2/Si$ substrates by the liquid delivery system MOCVD method. In these experiments, $Bi(ph)_{3}$, $Nd(TMHD)\_{3}$ and $Ti(O^iPr)_{2}(TMHD)_{2}$ were used as the precursors and were dissolved in n-butyl acetate. The BNdT thin films were deposited at a substrate temperature and reactor pressure of approximately $600^{\circ}C$ and 4.8 Torr, respectively. The microstructure of the layered perovskite phase was observed by XRD and SEM. The remanent polarization value (2Pr) of the BNdT thin film was $31.67\;{\mu}C/cm^{2}$ at an applied voltage of 5 V.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.131-136
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• 2009

Radio frequency (RF) plasma treatment is studied for the size reduction and the spheroidization of coarse particles to change them into nano-sized powders of spherical shape in MLCC fields. The uni-nanoadditives manufactured by RF plasma processing for high dispersion have been investigated for the effect on core-shell structure in dielectrics of MLCC. Microstructures have been characterized using scanning electron microscope (SEM), transmission electron microscope (TEM) and Electron Probe Micro Analyzer (EPMA). We compared the distribution of core-shell grains between specimens manufactured using uni-nanoadditive and using mixed additive. In addition, the uniformity of rare earth elements in the core-shell structured grains was analyzed. It was shown, from TEM observations, that the sintered specimen manufactured using uni-nanoadditives had more dense small grains with well-developed core-shell structure than the specimen using mixed additives, which had a homogeneous microstructure without abnormal grain growth and shows broad temperature coefficient of capacitance (TCC) curves in all temperature ranges because of well dispersed additives.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.25-28
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• 2001

The objectives of this paper are to demonstrate the electrical degradation phenomena with Si atom's behaviors in the grainboundary of semiconducting ZnO ceramics. The ZnO ceramic devices used in this investigation were fabricated by standard ceramic techniques. Especially, $SiO_2$ were added to analyze the degradation characteristics with Si and sintered in oxygen ambient at $1300^{\circ}C$. The conditions of DC degradation test were $115{\pm}2^{\circ}C$ for 13h. Using XRD and SEM, the phase and microstructure of samples were analyzed respectively. E-J analysis was used to determine $\alpha$. Frequency analysis was accomplished to understand $R_g$ and $R_b$ at the equivalent circuit. Electrical stability improved as the amount of $SiO_2$ addition increased. This results were explain by the quantitative analysis and the line scanning method of EPMA.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.126-129
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• 2003

The electrical properties of a ZnO-based multilayered chip varistor (abbreviated as MLV) were studied as functions of firing condition and the degree of lamination. The fundamental varistor characteristics such as nonlinear coefficient and breakdown voltage were independent of the degree of lamination. As the number of the laminated ceramic sheets increased, however, not only the energy handling capability but also the capacitance and the leakage current which are relevant to delayed response to the voltage surge and the pre-breakdown energy loss, respectively, increased. With the increase of firing temperature between $950^{\circ}C$ and $1150^{\circ}C$, both the capacitance and the leakage current of the MLV increased due mainly to the grain growth of ZnO and the volatilization of $BiO_2O_3$. High performance MLVs with clear electrode pattern were obtained at the firing temperature range of $l000{\sim}1050^{\circ}C$ in this experiment.

• Carbon letters
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• v.6 no.2
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• pp.71-78
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• 2005

Anti-oxidation coatings are the key technique for carbon/carbon (C/C) composites used as the thermal structural materials. The microstructure and oxidation behavior of several kinds of high-performance ceramic coatings for C/C composites prepared in Northwestern Polytechnical University were introduced in this paper. It showed that the ceramic coatings such as SiC, Si-$MoSi_2$, SiC-$MoSi_2$, $Al_2O_3$-mullite-SiC and SiC/yttrium silicate/glass coatings possessed excellent oxidation resistance at high temperatures, and some of these coatings were characterized with excellent thermal shock resistance. The SiC-$MoSi_2$ coating system has the best oxidation protective property, which can effectively protect C/C composites from oxidation up to 1973 K. In addition, the protection and failure reasons of some coatings at high temperature were also provided.

• Journal of the Korean Ceramic Society
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• v.36 no.7
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• pp.679-684
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• 1999

Specimens of SrZr0.95Ga0.05O3-$\delta$, SrZr0.95Y0.05O3-$\delta$, BaZr0.95Ga0.05O3-$\delta$ and BaZr0.95Y0.05O3-$\delta$ were fabricated by a solid-state reaction method and subsequent sintering at 150$0^{\circ}C$ to 1$600^{\circ}C$ The microstructures and electrical characteristics of the specimens were studied. Only BaZr0.95Ga0.05O3-$\delta$ showed dense microstructure and had typical impedance spectra at various temperature. Its electrical conductivity by impedance analysis was 2.7$\times$10-3$\Omega$-1.cm-1 at 90$0^{\circ}C$ in air. The BaZr0.95Ga0.05O3-$\delta$ exhibited lower grain rsistance in wet atmosphere than in dry atmosphere and the reduction of resistance is due to the proton conduction.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.553-560
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• 1997

A fine $\alpha$-Al2O3 powder was prepared by sol-gel process for membrane application. And it was carried out by adding 1.5wt% $\alpha$-Al2O3 powders(mean size : 87 nm) as seeds to the prepared sols and by controlling the heating schedule (the heating rate and the soaking time) to prevent the microstructural change, which occured during $\theta$-to $\alpha$Al2O3 phase transformation. The seeded $\alpha$-Al2O3 particles acted as the heterogeneous nucleation sites for the $\alpha$-Al2O3 nucleation during the transformation of $\theta$- to $\alpha$-Al2O3 and resulted in increasing the driving force of phase transformation to activate the formation of $\alpha$-Al2O3 phase at 82$0^{\circ}C$. By $\alpha$-Al2O3 seeding and controlling of heating condition the phase transformation of $\theta$- to $\alpha$-Al2O3 was accomplished at low temperature and the grain growth process was depressed. Therefore, the unsupported membrane could be fabricated in $\alpha$-Al2O3 . The average diameter of pores in the fabricated membrane was 7 nm and the porosity was 47%.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.583-590
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• 1997

The effects of Mn2O3 and Y2O3 additives on the microstructure and dielectric properties of Sr(Zr, Ti)O3 have been investigated. Powders with Sr(Zr1-xTix)O3(0$\leq$x$\leq$0.1) composition were prepared by the conventional solid state processing from commercial TiO2 and precipitation-processed ZrO2. The powders containing sintering additives of Mn2O3 and Y2O3 were compacted and then sintered at 1,55$0^{\circ}C$ for 4 h to get>97% relative density. Mn2O3 suppressed the grain growth and Y2O3 enhanced the density of sintered body. The oxidation state of Mn ions were determined by a chemical wet method and EPR spectroscopy. Mn ions were present as Mn2+ and Mn4+ in SrZrO3, while as Mn3+ and Mn4+ in Ti-substituted Sr(Zr, Ti)O3. With the substitution of Ti, the lattice parameters of SrZrO3 decreased and its dielectric constant increased with remarkable decrease in Q value. The dielectric constant of Sr(Zr, Ti)O3 was in the range of 30 to 40, Q values 1,200~5,400 at 6 GHz and temperature coefficient of resonant frequency -67~100 ppm/K.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.591-600
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• 1997

Al2O3/Al composites were produced by displacement reaction method, which was carried out by immersing the sintered silica preform, which was prepared from fused silica powder, in molten aluminum. Because the molten aluminum did not penetrate into the silica preform with higher than 20% of porosity when the displacement reaction was accomplished at 100$0^{\circ}C$ for 10 hours in air atmosphere, the optimum range of sintering temperature of silica preform was from 135$0^{\circ}C$ to 140$0^{\circ}C$. The microstructure of this Al2O3/Al composites showed three-dimentionally co-continuous alumina, which provides wear resistance and high stiffness, and aluminium which acts as a toughnening phase. The grain size of the alumina in composites did not change with the particle size of the silica preform. The exact shape of the preform was retained and a net-shaped composite was produced. The representative Al2O3/Al composite prepared in this study showed 3.30mg/㎤ of bulk density, 350-430 MPa of flexural strength, 7.0 MPa.m1/2 of fracture toughness, and good machinability.

• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.825-833
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• 1997

Silicon carbide films were deposited by low pressure chemical vapor deposition(LPCVD) using MTS(CH3SICl3) in hydrogen atmosphere on (100) Si substrate. To prevent the unstable interface from being formed on the substrate, the experiments were performed through three deposition processes which were the deposition on 1) as received Si, 2) low temperature grown SiC, and 3) carbonized Si by C2H2. The microstructure of the interface between Si substrates and SiC films was observed by SEM and the adhesion between Si substrates and SiC films was measured through scratch test. The SiC films deposited on the low temperature grown SiC thin films, showed the stable interfacial structures. The interface of the SiC films deposited on carbonized Si, however, was more stable and showed better adhesion than the others. In the case of the low temperature growth process, the optimum condition was 120$0^{\circ}C$ on carbonized Si by 3% C2H2, at 105$0^{\circ}C$, 5 torr, 10 min, showed the most stable interface. As a result of XRD analysis, it was observed that the preferred orientation of (200) plane was increased with Si carbonization. On the basis of the experimental results, the models of defect formation in the process of each deposition were compared.