• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.426-429
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• 2001

The $BaTiO_{3}+xNb_{2}O_{5}$[x=6, 8, 10wt%] ceramics were prepared by conventional mixed oxide method. The structural properties of the $BaTiO_{3}+xNb_{2}O_{5}$ ceramics with the sintering temperature and addition of $Nb_{2}O_{5}$ were investigated by XRD and SEM. Increasing the sintering temperature, the $2{\Theta}$ value of BT (110) peak was shifted to the lower degree and intensity of the BN (310) peak was increased. Increasing the addition of $Nb_{2}O_{5}$, the intensity of BN (100) peak was decreased and BN (310), (110) peaks were increased. The grain size of the $BaTiO_{3}+xNb_{2}O_{5}$ ceramics sintered at $1350^{\circ}C$ were almost uniform. In the $BaTiO_{3}+xNb_{2}O_{5}$ ceramics sintered at $1350^{\circ}C$, the dielectric constant and dielectric loss were 5424, 0.02 respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.426-429
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• 2001

The BaTiO$_3$+xNb$_2$O$_{5}$[x=6,8 , 10wt%] ceramics were prepared by conventional mixed oxide method. The structural properties of the BaTiO$_3$+xNb$_2$O$_{5}$ ceramics with the sintering temperature and addition of Nb$_2$O$_{5}$ were investigated by XRD and SEM. Increasing the sintering temperature, the 2$\theta$ value of BT (110) peak was shifted to the lower degree and intensity of the BN (310) peak was increased. Increasing the addition of Nb$_2$O$_{5}$, the intensity of BN (100) Peak was decreased and BN (310), (110) peaks were increased. The grain size of the BaTiO$_3$+Nb$_2$O$_{5}$ ceramics sintered at 135$0^{\circ}C$ were almost uniform. In the BaTiO$_3$+Nb$_2$O$_{5}$ ceramics sintered at 135$0^{\circ}C$, the dielectric constant and dielectric loss were 5424, 0.02 respectively.espectively.

• 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 Crystal Growth and Crystal Technology
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• v.15 no.4
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• pp.141-144
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• 2005

[ $(Y_{0.5}Sm_{0.25}Nd_{0.25})Ba_2Cu_3O_y$ ] [(YSN)-123] high $T_c$ composite superconductors with $CeO_2$ addition were systematically investigated by top seeded melt growth (TSMG) process in air atmosphere. A melt textured $NdBa_2Cu_3O_y$ (Nd-123) single crystal was used as a seed for achieving the c-axis alignment large grains perpendicular to the surface of (YSN)-123 composite oxides. The size of $(Y_{0.5}Sm_{0.25}Nd_{0.25})_2BaCuO_5$ [(YSN)211] nonsuperconducting inclusions of the melt textured (YSN)-123 samples with $CeO_2$ addition were remarkably reduced and uniformly distributed within the (YSN)123 superconducting matrix except in the region very close to the Nd-123 seed crystal. The sample showed a sharp superconducting transition of 91 K.

• 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 Ceramic Society
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• v.24 no.6
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• pp.579-585
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• 1987

The effects of flux KCl and dopant Nb2O5 on the PTCR characteristics of BaTiO3 prepared by molten salt synthesis method have been investigated. As the amount of dopant Nb2O5 is over the solubility limit in BaTiO3, the room-temperature resistivity increases, and the PTCR effect and the grain size decrease. The variation of the amount of flux KCl slightly influences on the room-temperature resistivity, PTCR effect and grain size in Nb2O5 doped BaTiO3, but BaTiO3 ceramics prepared by the method of molten salt synthesis show larger PTCR effect than those of conventional calcining of mixed oxides.

• Journal of the Korean Ceramic Society
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• v.30 no.6
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• pp.499-509
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• 1993

Structures of hematite(${\alpha}$-Fe2O3), Ba-ferrite(BaFe12O19) and Zn2Y(Ba2Zn2Fe12O22) were studied by powder X-ray diffraction(XRD) method. Powder XRD patterns of the ferrites were analyzed with the Rietveld method, and the final refined R-factors were RWP<0.01 and RI<0.03. The lattice parameters refined with hexagonal crystal system were a=5.0342${\AA}$, c=13.746${\AA}$ for hematite, a=5.8928${\AA}$, c=23.201${\AA}$ for Ba-ferrite, and a=5.8763${\AA}$, c=43.567${\AA}$ for Zn2Y. In the hematite, the oxygen parameter is 0.3072 and the Fe-O distances in FeO6octahedron are 1.941${\AA}$ and 2.118${\AA}$, close to the single crystal data of Blake et al.. In the Ba-ferrite, the Fe atom in oxygen trigonal bipyramid is displaced 0.155${\AA}$ away from the BaO3 mirror plane into 4e position. In the Zn2Y, 75% of Zn is located at the oxygen terahedral site in S-block.

• Journal of the Korean Ceramic Society
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• v.38 no.3
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• pp.245-250
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• 2001

BaO-TiO$_2$계의 TiO$_2$-rich 조성영역에 대한 상평형 관계를 완전 고상 반응법을 통하여 재평가하였다. 출발 시료로는 이 계의 end-member인 BaO와 TiO$_2$(rutile)를 이용하였다. 각 시료들은 대기 중에서 800~120$0^{\circ}C$의 온도구간에서 선택적으로 열처리되었다. 열처리된 시편들은 상온까지 급냉 처리되었으며, 상 분석은 X-ray 회절 분석을 통하여 이루어졌다. 연구결과에서 BaTi$_2$O$_{5}$(1:2)상과 BaTi$_{5}$O$_{11}$(1:5)상이 저온에서의 고상 반응을 통해서도 쉽게 형성될 수 있음을 알 수 있었으며, 각 저온 상들의 불변 반응 온도를 열처리 온도에 따른 상 분석을 통하여 확인할 수 있었다.

• 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$O_2$.