• Title, Summary, Keyword: $La_{2}O_{3}$

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Stable Defect Structure of La2O3-Modified BaTiO3 (La$_2O_3$-변형 BaTi$O_3$의 안정한 결함구조)

  • Kim, Jeong Su;Park, Hyu Beom;An, Tae Ho;Kim, Si Jung
    • 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$O_2$.

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Preparation of La0.5Nd0.5Ni5 Alloy by an Electrochemical Reduction in Molten LiCl (LiCl 용융염에서 전해환원법을 통한 La0.5Nd0.5Ni5 합금 제조)

  • Lim, Jong Gil;Jeong, Sang Mun
    • Korean Chemical Engineering Research
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    • v.53 no.2
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    • pp.145-149
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    • 2015
  • The electrochemical behavior of $Nd_2O_3-La_2O_3-NiO$ mixed oxide including rare earth resources has been studied to synthesize $La_{0.5}Nd_{0.5}Ni_5$ alloy in a LiCl molten salt. The $Nd_2O_3-La_2O_3-NiO$ mixed oxide was converted to $NiNd_2O_4$ (spinel) and $LaNiO_3$ (perovskite) structures at a sintering temperature of $1100^{\circ}C$. The spinel and perovskite structures led a speed-up in the electrolytic reduction of the mixed oxide. Various reaction intermediates such as Ni, $NiLa_2O_4$ were observed during the electrochemical reduction by XRD analysis. A possible reaction route to $La_{0.5}Nd_{0.5}Ni_5$ in the LiCl molten salt was proposed based on the analysis result.

Cation Ordering and Microwave Dielectric Properties of Complex Perovskite Compounds $La(Mg_{1/2}Ti_{1/2})O_3$ and $La(Mg_{1/2}Zr){1/2})O_3$ ($La(Mg_{1/2}Ti_{1/2})O_3$$La(Mg_{1/2}Zr){1/2})O_3$에서의 양이온 규칙과 고주파 유전특성)

  • 조서용;고경현;홍국선;박순자
    • Journal of the Korean Ceramic Society
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    • v.34 no.3
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    • pp.330-336
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    • 1997
  • 1:1 복합 페로스카이트 물질인 La(Mg1/2Ti1/2)O3 and La(Mg1/2Zr1/2)O3의 양이온 규칙 존재와 고주파 유전특성을 x선 회절과 회로망분석기를 사용하여 조사하였다. 기존의 연구에서는 두 물질 모두 양이온 규칙이 없으며 입방정 구조를 갖는다고 보고되었지만, 본 연구에서의 x선 분석에서는 양이온 규칙을 나타내는 초격자회절선과 비입방정 구조를 의미하는 기본회절선의 split이 발견되었다. 고주파 영역에서의 유전율은 La(Mg1/2Ti1/2)O3의 경우 29,La(Mg1/2Zr1/2)O3는 24, 품질계수(Q*f)는 각각 73000, 49000이다. 공진주파수 온도계수는 La(Mg1/2Ti1/2)O3의 경우 - 65ppm/$^{\circ}$C,La(Mg1/2Zr1/2)O3는 -80ppm/$^{\circ}$C로 음의 값을 가진다.

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Photoluminescence Behavior of $Al^{3+}$, $Pr^{3+}$ Doped Perovskite-type $La_{2/3}TiO_{3}and Pyrochlore-type $La_{2}Ti_{2}O_{7}$ ($Al^{3+}$, $Pr^{3+}$가 첨가된 Perovskite $La_{2/3}TiO_{3}와 Pyrochlore $La_{2}Ti_{2}O_{7}$의 발광 특성)

  • Park, Sang-Mi;Park, Joung-Kyu;Kim, Chang-Hae;Park, Hee-Dong;Jang, Ho-Gyeom
    • Journal of the Korean Ceramic Society
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    • v.38 no.9
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    • pp.806-810
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    • 2001
  • $La_{2/3}TiO_3$, $La_2Ti_2O_7$ are used in various parts by dielectric properties. The purpose of the present study is to understand the photoluminescence properties of $Al^{3+}\;and\;Pr^{3+}$ doped perovskite-type $La_{2/3}TiO_3$ and pyrochlore-type $La_2Ti_2O_7$ phosphor, which characterized by the red emission $(^1D_2{\rightarrow}^3H_4)\;of\;Pr^{3+}$ of $Pr^{3+}$ ion. The explanation for the energy transfer and the corresponding critical distance were proposed on the role of Al^3+ ions as energy transfer mediates in perovskite-type $La_{2/3}TiO_3$:Pr phosphor. In order to clarify the distinction of photoluminescence propoerties between the perovskite-type $La_{2/3}TiO_3$ and the pyrochlore $La_2Ti_2O_7$, the trap-involved process and the charge transfer band have been investigated.

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Sintering and Dielectric Characteristics of LaAlO3 Ceramics by Mechanochemical Treatment from La2O3-A12O3 and La2O3-Al(OH)3 (La2O3-Al2O3와 La2O3-Al(OH)3를 메카노케미칼로 처리한 LaAlO3세라믹스의 소결 및 유전특성)

  • 최상수;조정호;김강언;정수태;조상희
    • Journal of the Korean Ceramic Society
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    • v.39 no.1
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    • pp.68-73
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    • 2002
  • The dielectric properties and synthesis of $LaAlO_3$ ceramics from mixtures of $La_2O_3-Al_2O_3$ (LAO) and $La_2O_3-Al(OH)_3$(LAH) via grinding process were investigated. The single phase $LaA1O_3$of LAO and LAH powders were formed at $1300^{\circ}C$ and $1000^{\circ}C$, respectively. A non-reacted $La_2O_3$ existing in calcined powder was changed to La(OH)$_3$by moisture in the air, and their samples were worse than those of the samples made from a $LaA1O_3$single phase powder. The densities of LAO samples sintered at 150$0^{\circ}C$ for 4 h and LAH samples sintered at $1400^{\circ}C$ for 4 h were 97.3% and 98.3% of theory density, respectively. Grains of LAH sample showed uniformity and their sizes were 0.75 ${\mu}{\textrm}{m}$, and LAO samples showed non-uniformity and their sizes were 4-5 ${\mu}{\textrm}{m}$. Dielectric constant of LAO and LAH samples were the same value (≒22), however dielectric loss of LAH sample (0.0003) were lower than that of LAO sample(0.001)due to grain size.

Development of Pd/TiO2 Catalysts with La2O3 Addition and Study on the Performance Improvement of H2 Oxidation at Room Temperature (La2O3가 첨가된 Pd/TiO2 촉매의 개발 및 H2 상온산화 반응에서의 성능 향상 연구)

  • Lee, Dong Yoon;Kim, Sung Chul;Lee, Sang Moon;Kim, Sung Su
    • Applied Chemistry for Engineering
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    • v.31 no.6
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    • pp.674-678
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    • 2020
  • In this study, a Pd/TiO2 catalyst which oxidized H2 at room temperature without an additional energy source was prepared. And a specific surface area of TiO2 as a support was not proportional to H2 oxidation reaction performance of Pd/TiO2 catalyst. In addition La2O3 was added to Pd/TiO2 catalyst in order to evaluate the performance effect due to the change of catalysts physical properties. A Pd/La2O3-TiO2 was prepared by adding different amounts of La2O3 to TiO2 and CO chemisorption analysis was performed. Compared to the conversion rate (14% at 0.5% H2) of the Pd/TiO2(G) catalyst, the Pd/La2O3-TiO2 catalyst showed 74% which was improved by more than five times. It was found that the larger the metal dispersion of Pd as an active metal is, the more favorable to H2 oxidation reaction is. However, when the added La2O3 amount exceeded 10%, the catalyst performance decreased again. Finally, it was concluded that the physical properties of the Pd/La2O3-TiO2 catalyst have a dominant influence on the catalytic activity until 0.3~0.5% of injected H2 concentrations and the catalyst reaction rate was controlled by substance transfer from 1% or more concentrations of H2.

Gas Sensing Characteristics of La$_2$O$_3$-SnO$_2$Thick Film to COLa$_2$O$_3$-SnO$_2$ Gas (La$_2$O$_3$-SnO$_2$계 후막 소자의 $CO_2$감지특성)

  • 김동현;윤지영;박희찬;김광호
    • Journal of the Korean Ceramic Society
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    • v.36 no.3
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    • pp.301-306
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    • 1999
  • CO2 감지용 La2O3-SnO2 계 후막형 소자를 제조하여 CO2가스에 대한 기초 감지 특성을 조사하였고, 감지 분말의 입자크기와 제조방법에 따른 감도 변화를 고찰하였다. 후막 소자는 40$0^{\circ}C$의 작동온도와 4wt.%의 La2O3가 첨가되 srjt에서 가장 좋은 감도를 나타내었고, 낮은 습도영역에서 우수한 감지 특성을 보였다. 분말 혼합법에 의해 제조된 소자에 있어서 La2O3와SnO2 분말의 입자가 미세할수록 우수한 감도를 나타내었고, La2O3의 입도가 SnO2의 입도 보다 감도에 더 큰 영향을 주었다. SnO2 후막 표면에 La 용액을 코팅하여 제조된 센서는 가장 우수한 CO2 감도특성을 보였다.

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Toughening of $Al_2$O$_3$/LaAl$_{11}$O$_{18}$ Composites (Al$_2$O$_3$/LaAl$_{11}$O$_{18}$ 복합재료의 인성증진)

  • 장병국;우상국
    • Journal of the Korean Ceramic Society
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    • v.35 no.12
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    • pp.1266-1273
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    • 1998
  • Al2O3/(5~20vol%)LaAl11O18 composites in which the second phase was dispersed with a elongated grain shape were fabricated using Al2O3 and La2O3 composition by hot-pressing. In order investigate the in-fluence of LaAl11O18 on the toughening of LaAl11O18 on the toughening of Al2O3 matrix composites AE(acoustic emission) analysis was con-ducted together with an evaluation of fracture toughness using of SEPB technique. The degree of AE events occurred in composites were more than those in monolithic alumina. The occurrences of AE event increased with increasing the amount of LaAl11O18 phase in the Al2O3/LaAl11O18 composite is two times higher compared to monolithic alu-mina. The main toughening mechanism was attributed to the bridging of LaAl11O18 grains at tip of pro-pagating crack.

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Mechanochemical Synthesis of LaNiO3 Crystalline Phase from Mixture of La2O3sub> and NiO (La2O3의 메카노케미컬 합성에 의한 LaNiO3결정상 생성)

  • 김대영;김강언;이명교;정수태
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.16 no.8
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    • pp.681-687
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    • 2003
  • The syntheses of LaNiO$_3$Perovskite crystalline phase from mixtures of La$_2$O$_3$and NiO via it mechanochemical(used planetary mill) and a wet ball mill process were investigated. A single and stable LaNiO$_3$perovskite crystalline phase was successfully prepared by using a heat free mechanochemical process which produced a fine amorphous powder, while that phase was not formed in a wet ball mill process which needed heat treatment ranging from 500 to 150$0^{\circ}C$ and produced a coarse powder. It was shown that the LaNiO$_3$ceramics made of the mechanochemically synthesized powder possesed a good metallic characteristic.

Improvement in CO2 sensing characteristics using Pd nanoparticles decorated La2O3 thin films

  • Yadav, A.A.;Lokhande, A.C.;Kim, J.H.;Lokhande, C.D.
    • Journal of Industrial and Engineering Chemistry
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    • v.49
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    • pp.76-81
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    • 2017
  • $La_2O_3$ thin films are synthesized by spray pyrolysis method and decorated with palladium nanoparticles using successive ionic layer adsorption and reaction method. The structural and morphological properties of $La_2O_3$ and $Pd-La_2O_3$ are studied by X-ray diffraction, scanning electron microscopy, X-ray photo-electron spectroscopy and energy dispersive X-ray spectroscopy techniques. $CO_2$ gas sensing properties of $La_2O_3$ and $Pd-La_2O_3$ are investigated at different operating temperatures and $CO_2$ concentrations. $La_2O_3$ exhibited maximum response of 13% at 523 K upon exposure of $CO_2$ gas (500 ppm) which is improved up to 28% after Pd decoration. $Pd-La_2O_3$ film shows more selectivity towards $CO_2$ gas. Additionally, stability of $Pd-La_2O_3$ film has been studied.