• 한국재료학회:학술대회논문집
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• 한국재료학회 1999년도 춘계학술발표강연 및 눈문개요집
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• pp.68-68
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• 1999

• Corrosion Science and Technology
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• 제7권4호
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• pp.233-236
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• 2008

Halide-activated pack cementation was utilized to deposit B-doped silicide coating. The pack powders were consisted of $3Wt.c/oNH_4Cl$, 7Wt.c/oSi, $90Wt.c/oAl_2O_3+TiB_2$. B-doped silicide coating was consisted of two layers, an outer layer of $NbSi_2$ and an inner layer of $Nb_5Si_3$. Isothermal oxidation resistance of B-doped silicide coating was tested at $1250^{\circ}C$ in static air. B-doped silicide coating had excellent oxidation resistance, because continuous $SiO_2$ scale which serves as obstacle of oxygen diffusion was formed after oxidation.

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2002년도 추계총회 및 연구발표회 초록집
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• pp.41.2-41
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• 2002

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2002년도 추계총회 및 연구발표회 초록집
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• pp.170.2-170
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• 2002

• 한국재료학회:학술대회논문집
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• 한국재료학회 1997년도 한국재료학회 추계학술발표회
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• pp.141-141
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• 1997

• 한국세라믹학회지
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• 제32권9호
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• pp.967-976
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• 1995

The possiblity of the existence of a spontaneous relaxor-normal ferroelectric transition was proposed and examined using 1~5 mol% PbZrO3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 (PNN-PT) systems having tetragonal symmetry at rom temperature. On cooling, the system with 60mol% Pb(Ni1/3Nb2/3)O3 underwent a spontaneous transition from a relaxor to a normal ferroelectric state. A microscopic examination demonstrates that the relaxornormal ferroelectric transition corresponds to a micro-macro domain switching accompanied with thermoelastic martensitic transformation. The long-range macrodomains below the transition temperature were characterized by twinlike 90$^{\circ}$macrodomains with tetragonal symmetry. The relaxor-normal ferroelectric transition was further correlated with the rhombohedral-tetragonal first-order structural transition.

• 연구논문집
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• 통권25호
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• pp.185-192
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• 1995

The solid/liquid interface migration in Nb-doped $SrTiO_3$ and its effect on dielectric properties have been investigated. The specimen sintered in air shows no migration during oxide infiltration treatment in air, whereas the specimen sintered in $5H_2-95N_2$ shows appreciable migration during similar infiltration. In the migrated layers of the specimen sintered in a reducing atmosphere, no cations of the infiltrants are detected by wavelength dispersive spectroscopy. These results show that nonstoichiometry due to the atmosphere change can induce the interface migration as in the case of frequently observed migrations due to solute concentration change. The driving force for the migration is discussed in terms of the coherency strain energy in a thin diffusional oxidized layer of the receding grain. The interface migration caused by nonstoichiometry could be suppressed by preoxidizing grain surfaces before oxide infiltration treatment. The suppression of migration increased the effective dielectric constant of the material.

• 한국세라믹학회지
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• 제24권1호
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• pp.63-69
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• 1987

Effect of MoO3 additiion on the semiconductive BaTiO3 ceramics doped with 0.2 mole% Nb2O5 and their frequency characteristics have been investigated on the view of intergranular barrier layer model through the observation of changes in their electrical properties. The resistivity increases with the increase of MoO3 addition, but the capacitance, the frequency dependence of capacitance and the effect of positive temperature coefficient of resistivity (PTCR) decrease. It is explained by the possible increase in the thickness of potential barrier due to the formation of insulating layer and thus decrease in the degree of energy band bending. Both the PTCR effect and resistivity decrease with the increase of frequency due to the possible elimination of barrier layer at the grain boundary.

• 한국세라믹학회지
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• 제24권3호
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• pp.270-276
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• 1987

The microstructure and dielectric properties of a SrTiO3-based GBL (Grain Boundary Layer) capacitor were investigated. The 0.6 mol% Nb2O5 doped SrTiO3 was sintered for 3 hr at 1450$^{\circ}C$ in mixed gas(N2/H2) atmosphere. The Nb2O5 promoted the grain growth of the SrTiO3 ceramics was decreased with the amount of Nb2O5. The oxide mixture(PbO, Bi2O3, B2O3) were painted on the reduced specimen and fired at 1000$^{\circ}C$ to 1100$^{\circ}C$ in air. The penetrated oxide mixture into specimen were located in grain boundaries. A SrTiO3-based GBL capacitor had the apparent permittivity of about 3.0${\times}$104, the dielectric loss of 0.01-0.02, and insulating resistance of 108-109$\Omega$.cm. The capacitor had the stable temperature coefficient of capacitance and exhibited dielectric dispersion over 107 Hz. The capacitance-voltage measurements indicated that the grain boundary was composed of the continuous insulating layers.

• 한국재료학회지
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• 제18권9호
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• pp.475-481
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• 2008

Positive temperature coefficient of resistivity (PTCR) characteristics of (1-x)$BaTiO_3-x(Bi_{0.5}K_{0.5})TiO_3$ ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free PTC thermistor available at high temperatures of > $120^{\circ}C$. The PTCR characteristics appearing in the ($B_{i0.5}K_{i0.5})TiO_3$ (< 5 mol%) incorporated $BaTiO_3$ ceramics, which might be mainly due to $Bi^{+3}$ ions substituting for $Ba^{+2}$ sites. The 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics showed good PTCR characteristics of a low resistivity at room temperature (${\rho}_r$) of $31{\Omega}{\cdot}cm$ a high ${\rho}_{max}/{\rho}_{min}$ ratio of $5.38{\times}10^3$, and a high resistivity temperature factor (${\alpha}$) of $17.8%/^{\circ}C$. The addition of $Nb_2O_5$ to 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics further improved the PTCR characteristics. Especially, 0.025 mol% $Nb_2O_5$ doped 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics exhibited a significantly increased ${\rho}_{max}/{\rho}_{min}$ ratio of $8.7{\times}10^3$ and a high ${\alpha}$ of $18.6%/^{\circ}C$, along with a high $T_c$ of $148^{\circ}C$ despite a slightly increased ${\rho}_r$ of $31{\Omega}{\cdot}cm$.