• Title/Summary/Keyword: lanthanum

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Highly Donor-doped $Ba_{1-x}La_{x}TiO_{3}$ Semiconductive Ceramics

  • Soh, Dea-Wha;Korobova N.
    • Journal of information and communication convergence engineering
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    • v.1 no.1
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    • pp.31-34
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    • 2003

  • Sol-gel processing of $BaTiO_{3}$ ceramics doped with La (0.01∼1.00 at.%) were prepared from metal barium, titanium n-butoxide and lanthanum isopropoxide. Characterization of the sol-gel-derived powder using XRD, SEM is also reported. The obtained results suggested that insulator to semiconductor transition for highly donor-doped barium titanate was closely related to the incorporation of donor into the grains and to the resultant grain size, which were significantly affected by the sinterability of $BaTiO_{3}$ powders and sintering conditions used.

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Effect of Calcium Inhibitors on Mouse Oocyte Maturation ($Ca^{2+}$ Inhibitor가 생쥐난자 성숙에 미치는 영향)

  • Chung, Hye-Won;Yoo, Han-Ki;Bae, In-Ha
    • Clinical and Experimental Reproductive Medicine
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    • v.19 no.1
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    • pp.15-29
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    • 1992

  • In the present study, it was aimed to find the role of calcium on the maturation of mouse follicular oocytes as well as for the role of calcium inhibitors, $Ni^{2+}$ and $La^{3+}$. Mouse follicular oocytes were cultivated in different media at $37^{\circ}C$, in 100% humidified $CO_2$ incubator for 3 and 17 hrs. The results were as follows; 1. There was no differences in GVBD between the control and experimental groups during the 3 hr culture. 2. Mouse oocytes were matured to higher rate in MHBS rather than HTF for 17 hr culture. 3. Maturation rate was significantly lower in $Ca^{2+}$-free and $Ca^{2+}$ 0.4 mM which were tested, compared to other calcium concentration used in the present study. 4. Calcium inhibitor, $Ni^{2+}$, it showed highest degeneration rate at all calcium concentrations and additionally in $Ni^{2+}$ $100{\mu}M$ treated group next. Maturation rate was significantly decrease as the $Ca^{2+}$ inhibitor concentration increased. 5. In all Lanthanum treated groups of calcium-free, degeneration were significantly high treated groups at 0.4 mM $Ca^{2+}$ concentrations degeneration rates of all group were significantly lower than that of the control but maturation rates were not significantly different in any group. In lanthanum $100{\mu}M$ treated group at 0.4 mM and 0.8 mM calcium concentration, its maturation rate was significantly higher than that of the control. Maturation rates of all groups of lanthanum treated at 1.71 mM calcium concentration were not significantly different among groups. 6. In the calcium treated group (0.4mM-1.7 mM), the presence of phosphate does not seem to be needed for oocyte maturation. However, the presence of phosphate at $Ca^{2+}$ 0.8 mM only seems to stimulated maturation.

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Two-Dimensional Lanthanum-BDC Coordination Polymer:Hydrothermal Synthesis and Structure of [La4(BDC)6(H2O)5](H2O)(BDC=benzene-1,3-dicaboxylate) (2차원 La-BDC 배위 고분자: [La4(BDC)6(H2O)5](H2O)의 수열합성 및 구조(BDC=benzene-1,3-dicaboxylate))

  • Kim, Hye Jin;Min, Dong Won;Heo, Hyun Su;Lee, Soon W.
    • Journal of the Korean Chemical Society
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    • v.45 no.6
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    • pp.507-512
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    • 2001

  • The hydrothermal reaction between lanthanum(Ⅲ) nitrate $(La(NO3)3${\cdot}$6H_2O)$ and benzene-1,3-dicarboxylic acid $(H_2BDC)$ in the presence of 1,2-bis(4-pyridyl)ethane gave a 2-D lanthnum-BDC coordination polymer with an empirical formula of $〔La_4$(BDC)_6(H_2O)_5$〕(H_2O)$ (1). X-ray structure analysis of compound 1 revealed that this polymer contains four distinct La metals. The three La metals are 7-coordinate with three different structures: a capped trigonal prism, a capped octahedron, and a pentagonal bipyramid. The remaining La metal has a 8-coordinate, square antiprismatic structure.

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Sintering characteristics of monolithic ZrB$_{2 }$ and ZrB$_{2 }$-ZrC composit (단일상 ZrB$_{2 }$ 및 ZrB$_{2 }$- ZrC 복합체의 소결특성)

  • 김경훈;심광보
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.2
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    • pp.145-151
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    • 2000

  • The sintering behaviour of monolithic zirconium diboride (ZrB$_{2 }$) and ZrB$_{2 }$-based composite ZrB$_{2 }$-ZrC were studied using a pressureless sintering technique. The specimens were prepared using commercially available ZrB$_{2 }$ and ZrC powder which were pressed and subjected to pressureless sintering. The effects of lanthanum and neodymium used as sintering aids in the sintering processes were investigated. The sintered specimens were characterized using X-ray diffraction analysis and scanning electron microscopy. The ZrB$_{2 }$ specimen prepared using and addition of 1 wt% lanthanum and pressurelessly sintered at $2200^{\circ}C$ showed the maximum relative density of 96%. The ZrB$_{2 }$-ZrC composite specimen without the addition of any sintering aids exhibits the maximum sintered density but contains significantly detectable amount of secondary phase.

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