• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1684-1690
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• 2018

The layered semiconductors $Bi_2O_2Q$ (Q = S, Se) consists of $Bi_2O_2$ layers sandwiched by Q square nets. On the basis of density functional theory calculations, we examined the thermoelectric properties of $Bi_2O_2S$, $Bi_2O_2Se$ as well as hypothetical structure of $Bi_2O_2$($S_{0.5}Se_{0.5}$) consisting of mixed chalcogen nets. The thermoelectric power factor of $Bi_2O_2S_{0.5}Se_{0.5}$ is much greater than those of $Bi_2O_2S$ and $Bi_2O_2Se$, suggesting that introducing mixed chalcogen net in $Bi_2O_2Q$ is a possible way of enhancing the thermoelectric property of $Bi_2O_2Q$.

• 한국세라믹학회지
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• 제35권10호
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• pp.1107-1112
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• 1998

We could obtan c-axis oriented $SrBi_2$$Ta_2$$O_9$ thin films on usual Pt(111)/Ti/$SiO_2$/Si(100) substrate using a r. f. magnetron sputtering technique. According to the increase of sputtering pressure from 250 to 300 mTorr the Bi content and degree of the c-a xis preferred orientation of $SrBi_2$$Ta_2$$O_9$ thin films were increased. By controlling Bi(or $Bi_2O_3$) loss from $SrBi_2$$Ta_2$$O_9$ thin films during post annealing and by inserting $Bi_2O_3$ layer in $SrBi_2$$Ta_2$$O_9$ thin films the effect of Bi content on the c-axis oriented growth of $SrBi_2$$Ta_2$$O_9$ thin films could be investigated without the effect of sputtering pressure. The degree of the c-axis preferred orientation of $SrBi_2$$Ta_2$$O_9$ thin films was increased with increasing with increasing Bi content by control of Bi(or $Bi_2O_3$) loss of $SrBi_2$$Ta_2$$O_9$ thin films. But the c-axis oriented growth of $SrBi_2$$Ta_2$$O_9$ thin films disappeared by the inserting of $Bi_2O_3$ lay-er in $SrBi_2$$Ta_2$$O_9$ thin films.

• 한국재료학회지
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• 제3권4호
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• pp.410-421
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• 1993

Bi-Sr-Ca-O 초전도성계에서 $Bi_2O_3-(Sr_2CaCu_2O_x$)의 pseude binary계를 선택하여 $Sr_2CaCu_2O_x$에 $Bi_2O_3$를 5%단위로 40 cation mole% Bi까지 첨가하면서 $850^{\circ}C$ 초전도상 및 공존하는 상들의 평형 및 반응 경로들을 XRD, SEM, EDS, DTA를 이용하여 분석하였다. Bi의 함량이 35 mole% Bi보다 클 때에는 $Bi_2Sr_2CaCu_2O_8$상과 공존하는 액상이 형성되며 2212상의 액상으로 존재하며 액상의 냉각시 제일 먼저 $Bi_2Sr_2CaCu_2O_8$상 주의에 석출된 것이 관찰되었다.

• 한국세라믹학회지
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• 제26권4호
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• pp.479-486
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• 1989

According to the phase diagram, 6Bi2O3.GeO2 composition melts congruently at 93$0^{\circ}C$ and forms a stable ${\gamma}$-6Bi2O3.GeO2 crystal phase below the melting point. But when the melt of this composition was cooled at a rate 1-15$0^{\circ}C$/min without tapping by a glass rod or impurity addition, a metastable $\delta$-6Bi2O3.GeO2 crystal phase was formed. It is due to that as the nucleation energy barrier of $\delta$-6Bi2O3.GeO2 crystals, which have more open and defective structure, is lower than that of ${\gamma}$-6Bi2O3.GeO2 crystals. When impurities or ${\gamma}$-6Bi2O3.GeO2 crystals existed in the melt, stable ${\gamma}$-6Bi2O3.GeO2 crystal phase was formed at various cooling rate. It is because of that the impurities or the ${\gamma}$-6Bi2O3.GeO2 crystals role as a seed crystal and as a result the nucleation energy barrier of ${\gamma}$-6Bi2O3.GeO2 crystals is lowered.

• 한국세라믹학회지
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• 제26권1호
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• pp.139-145
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• 1989

An eutectic melt in the system(Bi2O3)0.85·(Nb2O5)0.15-6Bi2O3·SiO2 was unidirectionally solidfield at a rate of 0.5mm/h under a thermal gradient of 100℃/cm. Double crucibles and seed crystal plate were used in order to botain the composite crystals which had uniform microstructure throughout the ingot. The obtained composite crystals showed uniform microstructure, in which needle-like δ-(Bi2O3)0.85·(Nb2O5)0.15 crystals were arrayed in parallel in a matrix of γ-6Bi2O3·SiO2 single crystal. It was found that the <110> direction of δ-(Bi2O3)0.85·(Nb2O5)0.15 crystal was essentially parallel to the <111> direction of γ-6Bi2O3·SiO2 crystal in the composite crystals. A transverse thin plate of the composite crystals showed a high resolution optical transmission like an optical fiber array, and sharp chatoyancy was observed in the cabochon shaped composite crystals. Then, this may be useful for applications such as screen of a cathode ray tube or artificial cat's eye gem stones.

• 한국재료학회지
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• 제6권7호
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• pp.684-691
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• 1996

Bi-계 고온초전도체인 Bi2Sr2Ca2Cu3O10(Bi-2223)단일상을 반응시간을 줄이면서 합성하기 위하여 Bi-Sr-Ca-Cu-O계 내에 존재하는 Bi2Sr2Ca2Cu3O10(Bi-22o1), Bi2Sr2Ca2Cu3O10(Bi-2212), (Ca0.91Sr0.09)-CuO2의 혼합물, 특히 정확한 Bi1.7Pb0.4Sr2Ca2Cu3O10+x의 조성대신 (Ca0.91Sr0.09)CuO2가 많이 첨가된 조성의 혼합물에서 Bi-2223가 가장 쉽게 형성되었다. Bi-2223상은 86$0^{\circ}C$와 87$0^{\circ}C$에서 60시간 이내에 형성되었다. 소량의 Bi-2212상은 장시간의 반응후에도 여전히 존재하였다. 중간화합물을 이용한 합성방법이 통상의 소결방법에 비해 반응시간내에 소량의 불순물상들을 가진 Bi-2223상을 형성시킬 수 있다.

• 한국재료학회지
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• 제8권7호
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• pp.659-663
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• 1998

BaO.$Nd_{2}O_{3}$.$4TiO_{2}$세라믹스에서 Bi 치환위치 및 Bi 치환 량에 따른 상, 미세구조, 마이크로파 유전특성 등을 조사하였다. BaO.$Nd_{2}O_{3}$.$4TiO_{2}$ 세라믹스의 Nd 치환되어 $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$고용체 (0$\leq$x$\leq$0.2)를 형성하였다. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$에서 Bi 치환 량이 x=0에서 x=0.2까지 증가됨에 따라 입자크기가 계속 증가하였으며, 유전상수는 84에서 108까지 계속 증가하였고, 공진 주파수의 온도계수는 $44 ppm^{\circ}C$에서 $-30ppm^{\circ}C$로 계속 감소하였다. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$조성에서 Bi 치환 량이 x=0.04에서 0.08사이일 때 가장 양호한 마이크로파 유전특성이 얻어졌으며 이 때의 유전상수 (${\varepsilon}_r$)는 89~92, Q, f는 5855-6091 GHz, 그리고 공진 주파수의 온도계수 (${\tau}_f$)는 -7.7-7.5 ppm/$^{\circ}C$이었다.

• 한국세라믹학회지
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• 제35권10호
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• pp.1040-1048
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• 1998

Ferroelectric properties of{{{{ { { { {SrBi }_{2 }Ta }_{2-x }Nb }_{x }O }_{9 } }} (SBIN) thin films were affected by the amount of Bi content in SBTN. The addition of Bi into the SBTN films could be accomplished by heat treating SBTN/Bi2O3/SBTN het-erostructures fabricated by r.f. magnetron sputtering method. The variation of Bi content was controlled by changing the thickness of the sandwiched Bi2O3 in SBTN/Bi2O3/SBTN heterostructure from 50 to 400$\AA$. As changing the thickness of the sandwiched Bi2O3 in Bi2O3 films was increased from 0 to 100$\AA$ the grain grew faster and the ferroelectric pro-perties were improved. On the other hand when the thickness of Bi2O3 films was thicker than 150$\AA$ the fer-roelectric properties were deteriorated Especially for SBTN thin films inserted by 400$\AA$ Bi2O3 layer a Bi2Phase appeared as a second phase resulting in poor ferroelectric properties. The maximum remanent po-larization (2Pr) and coercive field(Ec) were obtained for the SBTN/Bi2O3/(100$\AA$)/SBTN thin films. In this case 2Pr and Ec were 14.75 $\mu$C/cm2 and 53.4kV/cm at an applied voltage of 3V respectively.

• 한국분말재료학회지
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• 제29권1호
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• pp.41-46
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• 2022

In this study, we report the microstructure and characteristics of Ag-SnO₂-Bi₂O₃ contact materials using a controlled milling process with a subsequent compaction process. Using magnetic pulsed compaction (MPC), the milled Ag-SnO₂-Bi₂O₃ powders have been consolidated into bulk samples. The effects of the compaction conditions on the microstructure and characteristics have been investigated in detail. The nanoscale SnO₂ phase and microscale Bi2O3 phase are well-distributed homogeneously in the Ag matrix after the consolidation process. The successful consolidation of Ag-SnO₂-Bi₂O₃ contact materials was achieved by an MPC process with subsequent atmospheric sintering, after which the hardness and electrical conductivity of the Ag-SnO₂-Bi₂O₃ contact materials were found to be 62-75 HV and 52-63% IACS, respectively, which is related to the interfacial stability between the Ag matrix, the SnO₂ phase, and the Bi₂O₃ phase.

• 공업화학
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• 제3권1호
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• pp.53-63
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• 1992

프로필렌을 선택산화시켜 아크로레인을 제조하는 반응을 Bi-molybdate 촉매상에서 고정층 반응기를 사용하여 연구하였다. ${\alpha}-Bi_2Mo_3O_{12}$위에 $MoO_3$를 담지시킨 M/BM-series 촉매는 함침법으로 제조되었고, 역으로 BM/M-series 촉매는 $MoO_3$위에 ${\alpha}-Bi_2Mo_3O_{12}$을 침전시켜 제조하였다. 또한 촉매의 특성분석을 위하여 질소흡착과 XRD, SEM을 이용하였다. M/BM-series 촉매에서는 $MoO_3$가 작은 입자로 분산되고 ${\alpha}-Bi_2Mo_3O_{12}$의 결정구조는 $MoO_3$상이 추가되어도 그 형상이 변하지 않는 채로 유지되었으나, BM/M-series 촉매의 표면형상 및 전체 구조는 촉매제조 중에 생기는 침전물인 $Bi(OH)_3$가 소성 도중 $MoO_3$와 반응하여 ${\alpha}-Bi_2Mo_3O_{12}$을 형성하는 관계로 그 조성에 따라 매우 불규칙적으로 변화하였다. 반응실험 결과, 두 종류의 촉매 모두에서 excess $MoO_3$가 포함되었을 때 활성이 크게 증가하였는데, 이는 선별산화반응이 주로 ${\alpha}-Bi_2Mo_3O_{12}$에서 일어나고 $MoO_3$는 ${\alpha}-Bi_2Mo_3O_{12}$에 산소 공급을 원활히 하여 활성을 증가시키기 때문으로 판명되었다. 또한 이러한 활성 증가는 ${\alpha}-Bi_2Mo_3O_{12}$와 기계적 혼합물 (mechanical mixture)에서도 관찰되었다.