• Korean Journal of Materials Research
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• v.5 no.4
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• pp.433-444
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• 1995

BaCe$O_{3}$를 첨가하여 용융공정으로 제조한 단결정형 Y$Ba_{2}$$Cu_{3}$$O_{x}$(1-2-3) 초전도체의 온도에 대한 자화특성을 연구하였다. 고상반응법과 용융공정으로 0에서 30wt% BaCe$O_{3}$를 1-2-3 결정내에 미세 분산시켰다. 초전도체의 자화특성은 VSM(vibrating sample magnetometer)을 사용하여 77K, 60K, 40K와 20K, 2 Tesla 자장범위에서 측정하였다. BaCe$O_{3}$를 첨가하지 않은 겨우나 5wt% BaCe$O_{3}$를 첨가한 1-2-3 결정의 경우, 77K, 외부자장이 증가시 자화율 차이가 증가하는 비정상 자화특성이 관찰된다. 측정온도가 60K에서는 제2차 최대점이 나타나는 자장값이 고자장쪽으로 이동한다. 20K와 40K의 저온에서는 비정상자화특성이 2 T의 자장범위까지 관찰되지 않았다. 15wt%와 20wt% BaCe$O_{3}$첨가한 시편에서는 자장이 증가하면 자화율차이가 단순히 감소한다. Y-Ba-Cu-O의 flux pinning 기구를 BaCe$O_{3}$첨가에 의한 미세조직변화로 설명하였다.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.737-746
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• 1989

After Ba-ferrite powders synthesized hydrothermally and its heated powders were dissolved partially with HCl treatment time, the BaO/Fe2O3 mole ratio of dissolved solutions and powders were measured by AAS, also, lattice constants, particle morphology and magnetic properties in HCl treated, heated and no-heated Ba-ferrite powders were abtained by means of XRD, SEM and VSM, respectively. From above analysis results, the effect of Ba/Fe mole ration in suspension(as starting material) on the BaO/Fe2O3 composition and particle characteristics of products were investigated, and the effect of heat treatment on magnetic properties of products examined. The composition, lattice constant and crystal phase of products depend on the Ba/Fe mole ratio in suspension. Ba content in surface or outer part of Ba-ferrite powder is higher than inner and heterogeneous, and the excess Ba ions in the inner part of particle move into the outer by heating, so that the mole ratio of BaO/Fe2O3 in the more jinner approaches more to the stoichiometric composition 1 : 6. The crystallinity, coercivity and saturation magnetization of products are increased by heat treatment, and the heat-treated samples synthesized hydrothermally in lower temperature are appreciated to have better powder characteristics.

• Journal of the Korean Ceramic Society
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• v.20 no.4
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• pp.340-346
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• 1983

The effect of aging coprecipitate obtained by the reaction of mixed solution 1.1 mol FeCl-0.1 mol $BaCl_2$ and 4.0 mol. NaOH-1.0 mol $K _2 CO_3$ on the synthesis process of Baferrite $(BaFe_{12}O_{19})$ was investigated by means of DTA, TGA, XRD and electron microscope. The no-aged coprecipitate seems to be the aggregate of amorphosus $Fe_3$ .$nH_2O$ and (1-X) $BaCO_3$.$xBa(OH)_2$, but the 30 days-aged to be composed of crystalline $Fe_2O_3H_2O$ and $BaCO_3$. The decomposition temperature of $BaCO_3$ in the coprecipitate increases from 400-$700^{\circ}C$ to 700-90$0^{\circ}C$ with increment of aging-time. In the no-aged coprecipitate Ba-ferrite is synthesized through the surface reaction of amorphous Fe_2O_3$ and skeleton crystal BaO at 800-90$0^{\circ}C$ with more compact crystalization. During calcination of the 30 days-aged coprecibitate the intermediate phase BaFe_2O_4$ is formed at 600-$700^{\circ}C$ and completely transformed to Ba-ferrite at 800-90$0^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.6
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• pp.495-500
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• 2009

The ceramic($BaTiO_3$)-polymer(epoxy) composites have been widely investigated as dielectric materials for embedded capacitors in printed circuit boards (PCBs). The dielectric properties of $BaTiO_3$/epoxy composites prepared using the agglomerated $BaTiO_3$ particles were investigated in the present study. The dielectric constants of the composites prepared using the agglomerated $BaTiO_3$ particles were about 2 times higher than those of the composites with the dispersed $BaTiO_3$ particles. The insulation resistance of the composites prepared using the agglomerated $BaTiO_3$ particles were lower than those of the composites with dispersed $BaTiO_3$ particles. As a result, there is tradeoff between high dielectric constant and insulation resistance in the $BaTiO_3$/epoxy composites. So it is important to select proper agglomerated or dispersed $BaTiO_3$ particles in accordance with needs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.111-115
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• 2000

$BaTIO_3$ thin films were prepared on (100) $BaTIO_3$ substrates by coating- pyrolysis process using metal-organic compounds of Ba and Ti. The amorphous films prefired at $450^{\circ}C$were crystallized above $700^{\circ}C$ under oxygen partial pressure of $2\times 10^{-4}$. The lattice parameters of the perpendicular axis for the $BaTIO_3$ thin films heat-treated below $800^{\circ}C$ were closer to a value of cubic $BaTIO_3$, whereas those above $800^{\circ}C$ were closer to a value of tetragonal BaTiG. The results of XRD P scan and pole-figure analyses indicated that BaTiO, thin films have an epitaxial relationship with the $SrTiO_3$ substrates. The $BaTIO_3$thin films annealed at$800^{\circ}C$ showed the surface with island-like grains about 0.4$mu \textrm{m}$ and the cross section of 0.8 $mu \textrm{m}$ thickness with granular grains.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.181-187
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• 1997

The layered BaTiO3 thin films with a high dielectric constant of polycrystalline BaTiO3 and a good in-sulating property of amorphous BaTiO3 were prepared. And their electrical properties were characterized with stacking methods. The BaTiO3 thin films were prepared by rf-magnetron sputtering technique using a ceramic target on Indium-doped Tin oxide coated glasses. A new stacking method resulted in higher dielec-tric constant, capacitance per unit area, and breakdown strength than those prepared by a conventional stacking method; the new method continuously decrease the substrate temperature after initial deposition of a polycrystalline BaTiO3 layer. The observed high dielectric constant could be explained only by a mul-tilayered amorphous/microcrystalline/polycrystalline structure, which was confirmed indirectly by AES depth profile.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.87-96
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• 2004

Polymer/ceramic composites are the most promising embedded capacitor material for organic substrates application. Predicting the effective dielectric constant of polymer/ceramic composites is very important for design of composite materials. In this paper, we measured the dielectric constant of epoxy/$BaTiO_3$ composite embedded capacitor films with various $BaTiO_3$ particles loading for 5 different sizes $BaTiO_3$ powders. Experimental data were fitted to several theoretical equations to find the equation useful for the prediction of the effective dielectric constant of polymer/ceramic composites and also to estimate the dielectric constant of $BaTiO_3$ powders. The Lichtenecker equation and the Jayasundere-Smith equation were useful for the prediction of the effective dielectric constant of epoxy/$BaTiO_3$ composites. And calculated dielectric constants of the $BaTiO_3$ powders were in the range of 100 to 600, which were lower than those of $BaTiO_3$ bulk ceramics.

• 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.

• The Journal of Engineering Research
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• v.2 no.1
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• pp.139-145
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• 1997

The effect of Ba addition on the thermal stabilization of $\gamma$-$Al_2O_3$ powders were studied. Ba additive was introduced into $\gamma$-$Al_2O_3$ powders by wet impregnation of $Ba(No_3)_3$.$6H_2O$. Ba additive was proved to be effective on the thermal stabilization of $\gamma$-$Al_2O_3$ powders by suppression of sintering. The optimum content of Ba was determined by 5 mol%, through the calcinations temperature range. It is suggested that the main reason of thermal stabilizaton is the substitution effect of large $Ba^{2+}$ ions into the $\Al^{3+}$ sites, which suppressed the surface diffusion of $\Al^{3+}$ ions.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.775-782
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• 1998

This experiment is third study concerning BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} (Ln=Sm, Nd, Pr, La..) system which is known to show a high dielectric constant and Q value in microwave dielectric materials. The process of cry-stallization and the microwave dielectric properties of the specimens sintered at 1220-140$0^{\circ}C$ for 2 hr was investigated in the BaO-(Na,{{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} as well as BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} system. The single phase BaPr2Ti5O14 and Ba(Nd,{{{{ { { Pr})_{2 }O }_{3 } }}Ti5O14 was finally formed from the Pr2Ti2O7 (Nd, Pr)2Ti2O7 as a secondary phase in the BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} and BaO-(Nd, {{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} system respectively The dielectric constant of the specimens sint-ered at 1280~131$0^{\circ}C$ showed the maximum value as 105(BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} system) and 88 (BaO-(Nd,{{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} system) and the Q values of them showed higher value than 1800 which are due to the maximum den-sity. However the dielectric properties of the specimens sintered at higher temperature than 131$0^{\circ}C$ were reduced due to the increases of pore which were resulted from the sudden grain growth.