• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.88-89
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• 2000

The properties for self-frequency doubling (SFD) is unique phenomena for a small number of special single crystals. It is known that there are serious limitations to vary the concentration of active ions, for example high doping of active ions from 1 to 50 atomic %, in nonlinear materials. Until now, the Nd:YAl$_3$(BO$_3$)$_4$ (YAB) and Nd:(Ce,Gd)Sc$_3$(BO$_3$)$_4$ (CSB) crystals with high doping rates are well studied for the application of SFD purpose. They have much useful SFD properties, but also have big problems in crystal growth. In case of YAB crystal, it can be grown by solution melt method with very low growth rates and easy occurrence of inclusions. In case of CSB crystal, it has optically heterogeneity problems because of disarrangement of ions in huntite structure [1]. These problems make above crystals not so attractive for optical applications. Some popular nonlinear materials, such as LiNbO$_3$(LN), KTiOPO$_4$(KTP), LiB$_3$O$_{5}$ (LBO) crystals, are impossible to substitute by Rare Earth activators because of their crystallo-chemical problems of structure. When we dope active ions with the requisite concentrations for laser generation, it results in decreasing of optical quality of crystals or destroying of acentrosymmetric structure. (omitted)d)

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.199-201
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• 1996

The design and manufacturing results of a 16 tesla/45mm bore superconducting magnet is presented. The system consists of an 8.2 tesla(at 4.2K) outer NbTi coil with a bore I.D. of 261mm, a winding O.D. of 453mm and the length of 430mm which is connected in series with a 5.6 tesla(at 4.2K) middle and a 4.7 tesla(at 4.2K) inner insert coil constructed of multifilamentary $Nb_3Sn$. The middle and inner insert coil are reacted after winding. Also, epoxy impregnation is accomplished at $Nb_3Sn$ coils using a low viscosity crack resistant epoxy which is forced into the coil with a series of vacuum and over atmosphere pressure cycle.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.407-407
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• 2008

무기EL 디스플레이는 고체재료에 전계를 가했을 때 발광하는 현상을 이용한소자로서, 급속도로 발전을 거듭하고 있으나, 유전체층에 강한전계를 가하여 발광하여야 하므로 낮은 Breakdown voltage와 효율의 한계로 인하여 휘도가 낮고 풀 컬러화 디스플레이 등 의 응용에는 적용되고 있지 못하는 실정이다. 본 연구에서는 강유전체 Perovskite 구조를 가지는 ABO3 물질 중 PMN(Lead Magnesium niobate) 과 PZT (Lead Zirconate titanate) 후막을 제조하여 Inorganic EL(Electro Luminance)에 적용하고 소자의 광전특성을 평가하였다. 소자에 사용된 기판은 고온소성에 알맞은 알루미나(Al2O3)기판을 채택 하였으며, 그 위 하부전극으로는 고온소성에 따른 화학적 안정성이 우수한 Au전극을 Screen Printing 하였다. 제조 되어진 PMN후막 페이스트는 PMN(Pb(Mg1/2 Nb2/3)O3) + Glass Frit(Pb-Zn-B) + BaTiO3(99.99%) 로 합성되었으며 하부전극위에 인쇄하였다. 그 다음 PZT sol-gel을 Spin coating으로 도포 하였다. 형광체로 ZnS:Cu.Cl 을 Screen Printing을로 형성하였으며, 평탄화를 위하여 유기물 충을 Screen Printing 공정으로 성막 하였다. 상부전극으로는 DC sputter로 ITO를 증착하여 EL소자 완성 후 Spectro - Chroma meter로 소자특성을 측정하였다. 평탄화를 통한 유기물층에 변화되는 Capacitance를 Oscilloscope로 전압 전류 pulse의 변화에 따른 opto-electronic 특성을 평가하였다.

• Journal of the Korean Ceramic Society
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• v.37 no.1
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• pp.12-20
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• 2000

Dielectric property of Ba-modified 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 ceramics having compositions near the morphotropic phase boundary was investigated. For the specimens having Ba contents between 0 and 20 at%, the average transition temperature was decreased linearly with increasing Ba contents and the degree of hysteresis was also decreased with increasing Ba contents. The maximum dielectric constants (K), electric field induced polarization(P) and electrically-induced strain(S) were found to exihibit a maximum value at∼3 at% of Ba. The increase of S and the decrease of hysteresis by minor additions of Ba impurities indicated the development of new higher perfomance actuator materials. The composition of Ba-PMN-PT (10/65/35) may be appropriate for capacitor materials because of low hysteresis and high polarization.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1175-1177
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• 2011

The SBN thin films were deposited on Pt/Ti/$SiO_2$/Si and p-type Si(100) substrate by rf magnetron sputtering method using $Sr_{0.7}Bi_{2.3}Nb_2O_9$ ceramic target. SBN thin films deposited were annealed at 600~800[$^{\circ}C$] by furnace in oxygen atmosphere during 40min. The polarization characteristics have been investigated to confirm the possibility of the SBN thin films for the application to destructive read out ferroelectric random access memory. The maximum remanent polarization and the coercive voltage are 0.6[${\mu}C/cm^2$], 1.2[V] respectively at annealing temperature of 800[$^{\circ}C$]. The leakage current density was the $2.57{\times}10^{-6}[A/cm^2]$ at an applied voltage of 5[V] at annealing temperature of 650[$^{\circ}C$]. Also, the fatigue characteristics of SBN thin films did not change up to $10^8$ switching cycles.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.23-30
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• 1997

Semiconductive SrTiO3 ceramic bodies were prepared by conventional ceramic powder processes in-cluding sintering in a reducing atmosphere. Sodium or potassium ions were diffused from the surface of the sintered bodies into the inner region using thermal diffusion process at 800-120$0^{\circ}C$. The effects of such ther-mal treatments on the electrical and chemical characteristics of the grain boundaries were investigated. The presence of sodium or potassium ions at grain boundaries produces non-linear current-voltage behaviors, electrical boundary potential barriers of 0.1-0.2eV, and threshold voltages of 10-70V. The diffused ions form diffusion layers with thicknesses of 20-50nm near the grain boundaries, reducing the concentration of strontium and oxygen.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.9
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• pp.692-701
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• 2012

Recently, many lead-free piezoelectric materials have been investigated for the replacement of existing Pb-based piezoelectric ceramics because of globally increasing environmental interest. There has been remarkable improvement in piezoelectric properties of some lead-free ceramics such as $(Bi,Na)TiO_3-(Bi,K)TiO_3-BaTiO_3$, $(Na,K)NbO_3-LiSbO_3$, and so on. However, no one still has comparable piezoelectric properties to lead-based materials. Therefore, new lead-free piezoelectric ceramics are required. $BiFeO_3$ has a rhombohedrally distorted perovskite structure at room temperature and a very high Curie temperature ($T_C$= 1,100 K). And a very large electric polarization of 50 ~ 60 ${\mu}C/cm^2$ has been reported both in epitaxial thin film and single crystal $BiFeO_3$. Therefore, a high piezoelectric effect is expected also in a $BiFeO_3$ ceramics. The recent research activities on $BiFeO_3$ or $BiFeO_3$-based solid solutions are reviewed in this article.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.128-135
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• 1998

The paper gives a brief introduction to protonic defects and their chemistry, thermodynamics and transport in oxides. The temperature dependence of the equilibrium concentration of protons is illustrated and compared for different acceptor-doped oxides. The difficulties of saturating as well as emptying the oxides of protons are discussed. In order to illustrate the possibility of lattice relaxation of defects, a conceptual study is made of a case where the enthalpy of dissolution of protons(water) at the cost of oxygen vacancies is assumed dependent on the concentration of vacancies. It is shown how this changes the behavior of hydration curves vs temperature and water vapour pressure. finally, a discussion is given on the water uptake in heavily oxygen deficient oxides; how water uptake may affect order-disorder in the oxygen sublattice and eventually lead to defective, disordered or ordered oxyhydroxides or hydroxides of potential interest as intermediate temperature proton conductions.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.502-508
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• 2020

This paper focuses on the electrical properties and stability against DC accelerated aging stress of ZnO-V₂O₅-MnO₂-Nb₂O₅-Bi₂O₃-Co₃O₄-Dy₂O₃ (ZVMNBCD) varistor ceramics sintered at 850 - 925 ℃. With the increase of sintering temperature, the average grain size increases from 4.4 to 11.8 mm, and the density of the sintered pellets decreases from 5.53 to 5.40 g/㎤ due to the volatility of V₂O₅, which has a low melting point. The breakdown field abruptly decreases from 8016 to 1,715 V/cm with the increase of the sintering temperature. The maximum non-ohmic coefficient (59) is obtained when the sample is sintered at 875 ℃. The samples sintered at below 900 ℃ exhibit a relatively low leakage current, less than 60 mA/㎠. The apparent dielectric constant increases due to the increase of the average grain size with the increase of the sintering temperature. The change tendency of dissipation factor at 1 kHz according to the sintering temperature coincides with the tendency of the leakage current. In terms of stability, the samples sintered at 900 ℃ exhibit both high non-ohmic coefficient (45) and excellent stability, 0.8% in 𝚫E_B/E_B and -0.7 % in 𝚫α/α after application of DC accelerated aging stress (0.85 E_B/85 ℃/24 h).

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.625-628
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• 1998

This paper presents the design method of a temperature stable stepped-impedance resonator using composite material. In this method temperature coefficient of dielectric constant $(\tau\varepsilon)$ and thermal expansion coefficient $(\alpha1)$ of dielectric material were considered. Ba(Zn1/3Nb2/3)O3 and CaZrO3 as composite material having opposite signs of temperature coefficient of dielectric constant were selected. The length of this resonator for the temperature stability of resonance frequency was calculated at 900MHz, 1.4㎓ and 1.9㎓. It was found that the ratio of the length of positive $\tau\varepsilon$ materal to the length of negative $\tau\varepsilon$ material is constant at various resonance frequencies.