• Proceedings of the Korean Ceranic Society Conference
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• 2003.04a
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• pp.42.2-42
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• 2003

• Journal of the Korean Ceramic Society
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• v.36 no.3
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• pp.325-331
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• 1999

SrWO4가 첨가된 (Sr1-xBax)(Mg1/3Nb2/3)O3의 마이크로파 유전특성에 관하여 조사하였다. 관찰된 조성영역에서 Sr(Mg1/3Nb2/3)O3과 Ba(Mg1/3Nb2/3)O3은 (Sr1-xBax)(Mg1/3Nb2/3)O3고용체를 형성하고 SrWO4의 첨가는 고용체의 소결성을 향상시켜 소결온도 155$0^{\circ}C$에서 상대밀도 97% 이상을 얻었다. 소결한 시편의 EDS분석결과, SrWO4의 첨가량이 많은 시편에서 2차상이 존재하는 것을 알수 있었다. 순수한 Sr(Mg1/3Nb2/3)O3에 SrWO4를 0.01 mole첨가하여 1550~1$600^{\circ}C$에서 소결한 시편의 유전특성은 $\varepsilon$r 30, Q$\times$fo$\geq$55000,$ au$f -23 ppm/$^{\circ}C$이었다. 0.01 mole SrWO4가 첨가된 (Sr1-xBax)(Mg1/3Nb2/3)O3 고용체의 유전율과 온도계숙가 x에 따라 점차적으로 계속 증가하였고 Q$\times$fo는 x$\leq$0.25에서 x에 따라 감소하고 x$\geq$0.3에서 다시 증가하였다. (Sr0.65Ba0.35)(Mg1/3Nb2/3)O3+0.01SrWO4의 조성을 갖는 시편에서 $\varepsilon$r 34.4, Q$\times$fo$\geq$55000,$\tau$f 0 ppm/$^{\circ}C$이었다.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.739-743
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• 2003

New quaternary compounds $ANb_2PS_{10}$ (A = Na, Ag) and $AuNb_4P_2S_{20}$ were synthesized and characterized. The structures of three compounds consist of one-dimensional infinite chains built by [$Nb_2S_{12}$] and [$PS_4$] units. Cation atoms are occupied within the van der Waals gap of sulfur atoms between infinite chains to make -S…$M^+$…S- contacts. There is only one Au atom site and so crystallographically a unit cell contains four equivalent Au atoms in $AuNb_4P_2S_{20}$. This is only the half of the numbers of Na or Ag atoms in $NaNb_2PS_{10}$ or $AgNb_2PS_{10}$. The ratio between $Nb_2PS_{10}$ matrix vs the cation is, therefore, 1 : 1 for Ag and Na, but it is 2 : 1 for Au. Mixed valency in Au or Nb was expected to balance the charge in the latter compound. The electronic structures calculated based on the extended Huckel tight-binding method show that $ANb_2PS_{10}$ (A = Ag, Na) are semiconducting, while $AuNb_4P_2S_{20}$ is metallic, which is not consistent with the experimental results of these three compounds that all exhibit semiconducting property. The result of calculation suggests that $AuNb_4P_2S_{20}$ might be a magnetic insulator. Magnetic measurement experiment exactly proved that the compound is a Slater antiferromagnetic material with the Neels' temperature of 45 K. It is recognized, therefore, that electronic structure analysis is very useful to understand the properties of compounds.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.43-46
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• 2000

$H_4Nb_6/O_{17}$/CdS nanocomposites which intercalated CdS particles, less than 0.8nm thickness, in the interlayer of $H_4Nb_6/O_{17}$ were prepared by the successive ion exchange reactions of $H_4Nb_6/O_{17}$ with $Cd^{2+}$ and $C_3H_7NH_3_+$, followed by the reaction with $H_2S$ gas. $H_4Nb_6/O_{17}$/CdS photocatalytically reduced $NO_3$￣ to $NO_2$￣ and $NH_3$in the presence of sacrificial hole acceptor such as methanol under visible light irradiation (wavelength>400nm), although unsupported CdS showed no noticeable photocatalytic activity for $NO_3$￣ reduction. The catalytic activity of $H_4Nb_6/O_{17}$/CdS greatly enhanced with co-doping of Pt particles in the interlayer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.268-269
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• 2007

In this study, the structural and microwave dielectric properties of the $Sr_5Nb_4O_{15}$ cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the $Sr_5Nb_4O_{15}$ ceramics were prepared by the conventional mixed oxide method and sintered at $1350^{\circ}C{\sim}1500^{\circ}C$. The bulk density, dielectric constant and quality factor of the $Sr_5Nb_4O_{15}$ ceramics were increased with increasing sintering temperature. In the case of the $Sr_5Nb_4O_{15}$ ceramics sintered at $1500^{\circ}C$ for 5h, the dielectric constant, quality factor and temperature coefficient of the resonant frequency (TCRF) were 22.35, 16,577GHz, +13.40ppm/$^{\circ}C$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.371-374
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• 2004

저온동시 소성용(low temperature co-fired ceramics, LTCC) 마이크로파 유전체을 만들기 위해 $Ca(Li_{1/4}Nb_{3/4})O_3$ 마이크로파 유전체 세라믹스에 zinc-borosililcate glass를 첨가하여 소결 특성과 마이크로파 유전 특성을 조사하였다. $Ca(Li_{1/4}Nb_{3/4})O_3$과 $0.7Ca(Li_{1/4}Nb_{3/4})O_3-0.3CaTiO_3$에 zinc-borosilicate를 $5{\sim}30wt%$ 첨가하여 소결한 결과 $875{\sim}925^{\circ}C$에서 동시 소성이 가능한 것으로 확인되었으며 zinc-borosilicate glass의 함량이 증가할수록 저온에서 소성이 가능하였지만 과량의 액상과 2차상이 형성되면서 유전율과 품질계수가 저하되는 경향을 나타내었다. $Ca(Li_{1/4}Nb_{3/4})O_3$에 5wt%의 zinc-borosilicate를 첨가하여 $900^{\circ}C$에서 소성한 결과 가장 우수한 유전 특성$(\epsilon_r=17.45,\;Q{\times}f_0=5487)$을 나타내었고, 유전율을 높이기 위해 $CaTiO_3$를 0.3mol% 첨가한 $0.7Ca(Li_{1/4}Nb_{3/4})O_3-0.3CaTiO_3$에 10wt%의 zinc-borosilicate를 첨가하여 $925^{\circ}C$에서 소성한 결과 가장 우수한 유전특성$(\epsilon_r=44.92,\;Q{\times}f_0=5567)$을 나타내었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.1
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• pp.32-37
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• 2006

Rare-earth niobates, ag (Ln = Y, La, Gd) are well-known self-activated phosphors due to charge transfer in $NbO^{3-}_4$ showing a broad and strong emission band in the spectral region around 410 nm. In order to find new blue and red phosphors for FED, $LaNbO_4$ : X (X = Bi, Eu) phosphors are prepared through solid-state reactions at high temperature. The optimum reaction condition for these phosphors to give maximum emission intensity is obtained when it is first fired at $1250^{\circ}C$ for 2 h followed by second firing at $1400^{\circ}C$ for 1 h. Under irradiation at 254 nm, $1mol\%\;Bi^{3+}$ doped $LaNbO_4$ phosphor shows strong blue emission band with a range of $420\~450nm$. Also $10mol\%\;Eu^{3+}$ doped $LaNbO_4$ phosphor shows the maximum emission intensity at about 610 nm. Emission peaks at $415\~460nm$, $530\~560nm$and $570\~620nm$are observed in phosphors below $10mol\%\;Eu^{3+}$ doped $LaNbO_4$. Similar results are obtained in cathodoluminescent property of these phosphors.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.165-167
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• 2002

NbTi/Cu superconducting wires were jointed inserting the NbTi filaments into Cu/NbTi sleeve and pressing it. When the NbTi filaments were inserted into Cu/NbTi sleeve, additional NbTi filaments were inserted together to increase the numbers of filaments in the hole of sleeve. Critical current of the joint of 28 filaments wires with 1.7 mm thickness of dimple was 450 A at 4.2K, 0.5T. Ic of the joint of 54 filaments wires with 2.0 mm thickness of dimple was 600 A at 4.2K, 2T. It is possible to manufacture MRI magnet by using these results.

• Bulletin of the Korean Chemical Society
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• v.20 no.8
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• pp.893-896
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• 1999

Novel citric acid based Ti, Nb and Ta precursors that are highly stable in the presence of water were developed. No alkoxides of Ti, Nb and Ta were utilized in the preparation, instead much less moisture-sensitive metallic Ti, NbCl5 and TaCl5 were chosen as starting chemicals for Ti, Nb and Ta, respectively. The feasibility of these chemicals as precursors is demonstrated in the powder synthesis of BaTi4O9, Y3NbO7 and LiTaO3. The water-resistant Ti precursor was employed as a new source of water-soluble Ti in the amorphous citrate method, and phase pure BaTi4O9 in powdered form was successfully synthesized at 800 ？. The Pechini-type polymerizable complex method using the water-resistant Nb and Ta precursors was applied to the synthesis of Y3NbO7 and LiTaO3, and both the powder materials in their pure form were successfully synthesized at reduced tempera-tures, viz. 500-700 ？. The remarkable retardation of hydrolysis of these water-resistant precursors is explained in terms of the partial charge model theory.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.1-5
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• 2021

Among elemental metals, niobium (Nb) has the highest superconducting transition temperature (T_c) at ambient pressure. Thus, Nb films have been used in superconducting electronics and radio frequency cavity applications. In this study, the depositional factors determining the crystallinity and T_c of Nb films were investigated. An Nb film grown at a sputtering temperature of 240℃ exhibited the maximum crystallinity of Nb and the minimum crystallinity of niobium oxide. X-ray photoelectron spectroscopy confirmed a maximum atomic percent of niobium and a minimum atomic percent of oxygen. A sputtering power of 210 W and a sputtering time of 50 min were the optimal conditions for Nb deposition, and the T_c of the optimized film (9.08 K) was close to that of bulk Nb (9.25 K). Transmission electron microscopy images of the thick film directly confirmed the removal of the typical in-plane compressive strain in the (110) plane caused by residual stress.