• Journal of the Korean Ceramic Society
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• v.24 no.5
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• pp.484-490
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• 1987

Diffusion coupling experiment was done to study expansion of body and soild reaction in BaCO3-TiO2 system. Specimen of BaCO3 and TiO2 was formed with Pt-mark's method. Each specimen was fired at interval of 25℃ from 900℃ to 1000℃ for 2hrs. After that, specimen was fixed with resin and polished. Product layers of specimen were observed with SEM and EDS. The result were following; 1. Diffusion component is Ba2+, which diffuse toward TiO2. 2. Large crack between layer of BaCO3 and Ba2TiO4 was generated because of difference of thermal expansion coefficient. 3. Ba2TiO4 is formed to TiO2 body by the reaction of BaTiO3 and BaO and its structure is very porous. 4. BaTiO3 changes immediately to Ba2TiO4 by the reaction of BaO. But BaTiO3 which formed by the reaction of TiO2 and Ba2TiO4 exsists as layer because the diffusion distance of Ba2+ is far.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.83-89
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• 1995

YBa2Cu3O7-$\delta$, Y2BaCuO5, and binary compounds in the Ba-Cu-O system with the nominal composition of Ba2CuO3, BaCuO2, Ba3Cu4O7, Ba3Cu5O8 were synthesized to investigate the heat evolutions and crystalline phases in the hydration reaction of orthorhombic YBa2Cu3O7-$\delta$ phase. The observed crystalline phases were YBa2Cu3O7-$\delta$, Y2BaCuO5, and BaCuO2, or Ba2Cu3O5＋x, and some amount of noncrystalline phase in the Ba-Cu system comounds. In contact with distilled water, YBa2Cu3O7-$\delta$ and Y2BaCuO5 did not have considerable heat liberation, but in the binary compounds of the Ba-Cu-O system, the amount of total heat liberation was increased with respect to the Cu content. It might be that the reaction of high temperature superconductor YBa2Cu3O7-$\delta$ with water and/or moisture originated from the unusual oxidation state of Cu ion and the presence of amorphous Ba-Cu oxide compound. The degradation of high Tc superconductor by moisture and water could be controlled by restricting the heterogeneous distribution of Tc comlposition and the formation of second phase, such as stable Y2BaCuO5, and the resulting unstable Ba-Cu oxide compound.

• 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.

• The Journal of Natural Sciences
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• v.8 no.1
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• pp.61-69
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• 1995

It is hard to synthesize pure $BaTiO_3$ from $BaCO_3$ and $TiO_2$ in solid reaction for the activity of BaO and secondary phase. For this reason, the wet chemical techniques have been studied. Starting material which was used in these methods were expensive and the properties of powder which was synthesized in same defined. So, some process have been studying again to improve soild reaction method. This study which was one of those was to defin the forming mechanism of $Ba_2TiO_4$ and to control some condition of $Ba_2TiO_4$. The synthesis temperature of $BaTiO_3$ in solid reaction was near $1120^{\circ}C$. The quantity and forming temperature of $Ba_2TiO_4$ could be controlled by atmosphere heat treatment. $Ba_2TiO_4$ was related to expansion in Ba-rich region of $BaTiO_3$. $BaTiO_2O_5$ and $BaTiO_3O_7$ was reason to expand in Ti-rich region. The dielectrics of $CeAIO_3$ which was synthesized and sintered in reduction atmosphere and $BaTiO_3$ system were affected by $CeO_2$ which was formed for the decomposition of $CeAIO_3$ heat treatment in air.

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.1038-1044
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• 1996

The variations of sintering and electrical characteristics of semiconducting BaTiO3 ceramics with sintering agents added were investigated comparing the case of BaB2O4 addition to BN and TiO2 addition. When BaB2O4 added in BaTiO3 ceramics the densitifcation of specimen could be acheived more easily and recvealed the better PTCR characteristics than BN and TiO2 addition. As increase of addition of BaB2O4 in BaTiO3 spec imens the slope of resistivity jump also increased but the temperature of maximum resistivity decreased, It was supposed that addition of BaB2O4 led to increase of Ns (acceptor state density) value at grain boundaries.

• Electrical & Electronic Materials
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• v.10 no.8
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• pp.819-829
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• 1997

The microwave dielectric materials of the BaO-Nd$_2$O$_3$-TiO$_2$and BaO-(Sm, Nd)$_2$O$_3$-TiO$_2$system were synthesized by conventional ceramic processing and sintered 1220 to 140$0^{\circ}C$ for 2 hours respectively. Their crystallization and dielectric properties were examined. In the BaO-Nd$_2$O$_3$-TiO$_2$ and BaO-(Sm, Nd)$_2$O$_3$-TiO$_2$system. Nd$_2$Ti$_2$O$_{7}$ and (Sm, Nd)$_2$Ti$_2$O$_{7}$ were observed as a second phase respectively. The maximum relative dielectric constant were 79,99 for the BaO-Nd$_2$O$_3$-TiO$_2$system and 105.07 for the BaO-(Sm,Nd)$_2$O$_3$-TiO$_2$system and their Q-value were over 2000 at 3GHz.GHz.

• Journal of the Korean Chemical Society
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• v.25 no.5
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• pp.318-324
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• 1981

The effects of$ Fe_2O_3$ aggregation on the sintering of Ba-ferrite (BaFe$_{12}O_{19}$) were studied. $BaCO_3-Fe_2O_3$ mixtures were prepared by partial precipitation mixing and ball-mill mixing method using two different $Fe_2O_3 $powders. Techniques employed were TG, XRD and SEM. X-ray diffraction analysis showed that the over all reaction basically consists of the two consecutive reaction; $BaCO_3 + 6Fe_2O_3\;{\longrightarrow}\;BaFe_2O_3 + 5Fe_2O_3 + CO_2{\uparrow}\;BaFe_2O_4 + 5Fe_2O_3 \;{\longrightarrow}\;BaFe_{12}O_{19}$ It is also shown that the aggregation state of $Fe_2O_3$ raw materials, as well as the mixing method, has a remarkable effect on solid state reaction between $BaCO_3\;and\;Fe_2O_3$.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1005-1011
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• 1994

The three different composition of BaTi4O9, Ba2Ti9O20 and BaTi5O11 were prepared by coprecipitation process, and then the dielectric properties of these compounds were measured at low microwave frequencies. The powder showing high level of purity was synthesised by the coprecipition reaction of BaCl2 and TiCl4 where (NH4)2CO3 and NH4OH were used as a deflocculent. Followings are the result of this study: 1. The sintering temperature increased with increasing TiO2 content. 2. BaTi4O9 powder were synthesized as a single phase by this processing technique, but the resultant Ba2Ti9O20 and BaTi5O11 phase existed with Ba2Ti9O20 and BaTi5O11 phases. 3. Single phase BaTi4O9 showed high dielectric constant value of 35, high Q value of 8100.

• Bulletin of the Korean Chemical Society
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• v.16 no.3
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• pp.248-251
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• 1995

The crystal structure of Ba46-X, Ba46Al92Si100O384 [a= 25.297(1) Å], has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd&bar{3}at 21(1) ℃. The crystal was prepared by ion exchange in flowing stream of 0.05 M Ba(OH)2 aqueous solution for 5 days. The crystal was then dehydrated at 380 ℃ and 2 × 10-6 Torr for 2 days. The structure was refined to the final error indices R1= 0.051 and Rw= 0.054 with 369 reflections for which I > 3σ(I). In this structure, all Ba2+ ions are located at the three different crystallographic sites: fourteen Ba2+ ions are located at site Ⅰ, the centers of the double six rings, two Ba2+ ions lie at site Ⅰ', in the sodalite cavity opposite double six rings(D6R's) and another thirty Ba2+ ions are located at site Ⅱ in the supercage. Two Ba2+ ions are recessed ca. 0.27 Å into the sodalite cavity from their three O(3) oxygen plane and thirty Ba2+ ions are recessed ca. 1.11 Å into the supercage from their three O(2) oxygen planes, respectively (Ba(1)-O(3) = 2.76(1) Å, O(3)-Ba(1)-O(3) = 180(0)°, Ba(2)-O(3) = 2.45(1) Å, O(3)-Ba(2)-O(3) = 108(1)°, Ba(3)-O(2)=2.65(1) Å, and O(2)-Ba(3)-O(2)=103.9(4)°).

• Journal of the Korean Chemical Society
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• v.38 no.4
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• pp.309-318
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• 1994

The stable defect structure and the single phase region of La$_2O_3$-modified BaTi$O_3$ have been studied by X-ray diffractometer and scanning electron microscope. The stable defect structure of La$_2O_3$-modified BaTi$O_3$ has been identified as [($Ba^x_{Ba})_{1-2x}(La{\cdot}_{Ba})_{2x}][Ti^x_{Ti})_{1-x/2}(V""_{Ti})_{x/2}]O_3$ which consists of La$^{3+}$ ion substitution for Ba$^{3+}$ ion in the lattice structure and the formation of Ti vacancies for the charge compensation. When 3 mol% of La$_2O_3{\cdot}3/2TiO_3$ was added to BaTi$O_3$, the unit cell structure was transformed from tetragonal to cubic and the solubility limit was about 14 mol%. When La$_2O_3{\cdot}3/2TiO_2$ was added above this solubility limit, the second phase, La$_4Ba_2Ti_5O_{18}$, was formed. In the La$_2O_3$-modified BaTi$O_3$, it was found by the liquid phase sintering process that the sinterability was decreased by excess BaO but increased by excess Ti$O_2$.