• Title/Summary/Keyword: $LaA1O_3$

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Crystal structure refinement and microwave dielectric characteristic of $(1-x)CaTiO_3-x(La_{1/3}Nd_{1/3})TiO_3$ ($(1-x)CaTiO_3-x(La_{1/3}Nd_{1/3})TiO_3$계의 결정구조 해석 및 마이크로파 유전 특성)

  • 조남웅;성경필;문종하;최주현
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.8 no.3
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    • pp.478-486
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    • 1998
  • $CaTiO_3-x(La_{1/3}Nd_{1/3}TiO_3\;(0\le \textrm x\le0.8)$ system was prepared by reaction of $CaCO_3,\;LaO_3,\;Nd_2CO_3$ and ,TEX>$TiO_2$ mixture at 1673 K, which can be applied for microwave dielectric ceramic materials. The lattice parameters of(1-x))$CaTiO_3-x(La_{1/3}Nd_{1/3}TiO_3\;(0\le \textrm x\le0.8)$ system increased with the increase of x. Its structure was investigated by Rietveld profile-analysis of XRD in detail. Cations $ La^{3+}$ and Nd^{3+}$ were located at the $Ca^{2+}$ site in the range of $0\le \textrm x\le0.8$. crystal structure in $;(0\le \textrm x\le0.6)$ maintained space group Pnma with CaTiO_3 structure. The tiled and distorted $TiO_6$ was gradually released with the increase of x in $0\le \textrm x\le0.6$ .The structure was changed to a new space group of $Pmn2_1$ at the x value of 0.8. The relative dielectric constant $(\epsilon_r)$ of $(1-x)CaTiO_3-x(La_{1/3} Nd_{1/3})TiO_3$ ($(0\le \textrm x\le0.8)$) system was exponentially decreased by with the increased of x. The temperature coefficient of resonant frequency $(\tau_f)$ decreased with the increase of x in $0\le \textrm x\le0.6$ and then increased again at x=0.8 due to the change of crystal structure. The value of Q$\cdot f_o$ was 13800 (GHz) at x=0.2 and was very low under 2000 (GHz) in 0.4$\leq$x$\leq$0.8.

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Investigation of LiO2 Adsorption on LaB1-xB'xO3(001) for Li-Air Battery Applications: A Density Functional Theory Study

  • Kwon, Hyunguk;Han, Jeong Woo
    • Journal of the Korean Ceramic Society
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    • v.53 no.3
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    • pp.306-311
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    • 2016
  • Li-air batteries have received much attention due to their superior theoretical energy density. However, their sluggish kinetics on the cathode side is considered the main barrier to high performance. The rational design of electrode catalysts with high activity is therefore an important challenge. To solve this issue, we performed density functional theory (DFT) calculations to analyze the adsorption behavior of the $LiO_2$ molecule, which is considered to be a key intermediate in both the Li-oxygen reduction reaction (ORR) and the evolution reaction (OER). Specifically, to use the activity descriptor approach, the $LiO_2$ adsorption energy, which has previously been demonstrated to be a reliable descriptor of the cathode reaction in Li-air batteries, was calculated on $LaB_{1-x}B^{\prime}_xO_3$(001) (B, B' = Mn, Fe, Co, and Ni, x = 0.0, 0.5). Our fast screening results showed that $LaMnO_3$, $LaMn_{0.5}Fe_{0.5}O_3$, or $LaFeO_3$ would be good candidate catalysts. We believe that our results will provide a way to more efficiently develop new cathode materials for Li-air batteries.

Microwave Dielectric Properties of $[(Pb_{1-x}Ba_{x})_{1/2}La_{1/2}](Mg_{1/2}Nb_{1/2})O_{3}$ Ceramics ($[(Pb_{1-x}Ba_{x})_{1/2}La_{1/2}](Mg_{1/2}Nb_{1/2})O_{3}$의 마이크로파 유전 특성)

  • Lee, Sang-Wook;Nam, Hyo-Duk;Park, Jae-Sung;Seo, Jung-Chul;Kim, Jong-Chul
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11b
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    • pp.476-479
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    • 2001
  • The microwave dielectric properties of $[(Pb_{1-x}Ba_{x})_{1/2}La_{1/2}](Mg_{1/2}Nb_{1/2})O_{3}$ ceramics were investigated. When $[(Pb_{0.9}Ba_{0.1})_{1/2}La_{1/2}](Mg_{1/2}Nb_{1/2})O_{3}$ ceramics were sintered at $1250^{\circ}C$ and $1350^{\circ}C$ for 2hr, the microwave dielectric properties were obtained $\varepsilon_{r}=64\sim80$, $Q{\times}f=11,800\sim18,000$. As a result, $[(Pb_{0.9}Ba_{0.1})_{1/2}La_{1/2}](Mg_{1/2}Nb_{1/2})O_{3}$ having $\varepsilon_{r}=80$, $Q{\times}f=11,800$ (at 4 GHz) was developed.

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Microwave Dielectric Properties of [($Pb_{1-x}Ba_{x}$)$_{1/2}La_{1/2}$]($Mg_{1/2}Nb_{1/2}$)$O_3$ Ceramics ([($Pb_{1-x}Ba_{x}$)$_{1/2}La_{1/2}$($Mg_{1/2}Nb_{1/2}$)$O_3$의 마이크로파 유전 특성)

  • 이상욱;남효덕;박재성;서정철;김종철
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11a
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    • pp.476-479
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    • 2001
  • The microwave dielectric properties of [(Pb$_{1-x}$ Ba$_{x}$)$_{1}$2/La$_{1}$2/](Mg$_{1}$2/Nb$_{1}$2/)O$_3$ ceramics were investigated. When [(Pb$_{0.9}$Ba$_{0.1}$)$_{1}$2/La$_{1}$2/](Mg$_{1}$2/Nb$_{1}$2/)O$_3$ ceramics were sintered at 125$0^{\circ}C$ and 135$0^{\circ}C$ for 2hr, the microwave dielectric properties were obtained $\varepsilon$$_{r}$=64~80, Qxf=11,800~18,000. As a result, [(Pb$_{0.9}$Ba$_{0.1}$)$_{1}$2/La$_{1}$2/](Mg$_{1}$2/Nb$_{1}$2/)O$_3$ having $\varepsilon$$_{r}$=80, Qxf=11,800 (at 4 GHz) was developed.ed.eveloped.ed.

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Oxygen Reduction Reaction of La1-xCaxCoO3 of Gas Diffusion Electrode in Alkaline Fuel Cell (알칼리형 연료전지용 La1-xCaxCoO3 기체확산전극의 산소환원반응)

  • Shim, Joong-Pyo;Park, Yong-Suk;Lee, Hong-Ki;Park, Soo-Gil;Lee, Ju-Seong
    • Applied Chemistry for Engineering
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    • v.7 no.5
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    • pp.992-998
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    • 1996
  • The $La_{0.8}Ca_{0.2}CoO_3$ prepared by a citrate process was shown to have higher oxygen reduction current density and specific activity than $LaCoO_3$, $La_{0.6}Ca_{0.4}CoO_3$. In the cyclic voltammogram, an oxygen desorption peak of a $La_{0.8}Ca_{0.2}CoO_3$+carbon electrode was larger than that of a only carbon electrode. $La_{0.8}Ca_{0.2}CoO_3$ sintered at $900^{\circ}C$ for 5 hours was shown high oxygen reduction current density because of the particle size distribution and sintering effect.

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Microwave Dielectric Characteristics of the $xMgTiO_3$(1-x) ($Na_{1/2}Ln_{1/2}$) $TiO_3$(Ln = La, Pr, Nd, Sm)Systems ($xMgTiO_3$(1-x) ($Na_{1/2}Ln_{1/2}$) $TiO_3$(Ln = La, Pr, Nd, Sm)의 초고주파 유전특성에 관한 연구)

  • Kim, Duck-Hwan;Lim, Sang-Kyu;An, Chul
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.10
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    • pp.51-59
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    • 1998
  • ($Na_{1/2}Ln_{1/2}$)$TiO_3$ceramics have a high relative dielectric constant and a positive temperature coefficient of resonant frequency ($\tau_f$)(where Ln represents a lanthanide: $La^{+3}$, $Pr^{+3}$, $Nd^{+3}$ and $Sm^{+3}$). On the other hand, $MgTiO_3$ ceramic has a high Qf value and a negative temperature coefficient. So We have investigated the microwave dielectric properties of $xMgTiO_3$-(1-x) ($Na_{1/2}Ln_{1/2}$)$TiO_3$. In these systems, there are no clues on solid-solution and secondary phase. There are mixed phases with $MgTiO_3$and ($Na_{1/2}Ln_{1/2}$)$TiO_3$ phases. Its dielectric characteristics (Qf, temperature coefficient and dielectric constant) are intermediate between ($Na_{1/2}Ln_{1/2}$)$TiO_3$ and $MgTiO_3$ and are predictable by the logarithmic mixing rule. The dielectric ceramic compositions temperature coefficient each approximates to zero at Ln=La, x=0.9, Ln=Pr, x=0.87, and Ln=Nd, x=0.84. At this time, there are Qf values in the range of 55,000 to 28,00GHz and relative dielectric constants in the range of 22 to 25.

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High Temperature Thermal Conductivities in La2Ce2O7−Gd2Ce2O7−Y2Ce2O7 Pyrochlore System for Thermal Barrier Coatings (열차폐코팅용 La2Ce2O7−Gd2Ce2O7−Y2Ce2O7 Pyrochlore계의 고온 열전도도)

  • Yoon, So-Young;Lee, Sung-Min;Shim, Kwang-Bo;Kim, Hyung-Tae
    • Journal of the Korean Ceramic Society
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    • v.44 no.7
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    • pp.387-392
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    • 2007
  • Thermal conductivities in $La_2Ce_2O_7-Gd_2Ce_2O_7-Y_2Ce_2O_7$ ternary system have been investigated. Pyrochlore phases formed at all ternary compositions and their sinterbilities were decreased with La addition. Thermal conductivities showed a minimum value at $La_2Ce_2O_7$ with moderate increases as $Y^{3+}$ and $Gd^{3+}$ ions replaced $La^{3+}$. Thermal expansion anomaly observed in $La_2Ce_2O_7$, which might be detrimental to TBC application, were suppressed by $Y^{3+}$ and $Gd^{3+}$ additions, with resultant thermal conductivities, $1.3{\sim}1.5 W/mK$ at $1000^{\circ}C$.

Dielectric and Magnetic Properties of BaTiO3-LaMnO3 Composites

  • Kim, N.G.;Koo, Y.S.;Jung, J.H.
    • Journal of Magnetics
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    • v.11 no.4
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    • pp.164-166
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    • 2006
  • We have investigated the dielectric and magnetic properties of ferroelectric-antiferromagnetic $BaTiO_{3}-LaMnO_{3}$ composite with changing relative mole percents. Due to high sintering temperature, i.e. $1150^{\circ}C$, the Ba ion in $BaTiO_{3}$ seems to diffuse into $LaMnO_{3}$; resulting in $BaTiO_{3}-(La,Ba)MnO_{3}$ ferroelectric-ferromagnetic composite. At room temperature, $0.9BaTiO_{3}-0.1LaMnO_{3}$ composite exhibits considerable magnetization (${\sim}0.7\;emu/g\;at\;2000\;Oe$) and low coercive field (${\sim}5\;Oe$). Also it exhibits high dielectric constant (${\sim}560$) and low loss (${\sim}0.08$) at 10 kHz. This result may imply that $BaTiO_{3}-LaMnO_{3}$ could be suitable for a low leakage multiferroic composite.

Fabrication and Characterization of Cr Alloy for Metallic Interconnect of Solid Oxide Fuel Cell (고체 산화물 연료전지용 Cr계 금속 연결재 제조 및 특성 연구)

  • Song, Rak-Hyun
    • Journal of Hydrogen and New Energy
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    • v.16 no.1
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    • pp.58-65
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    • 2005
  • The $LaCrO_3$-dispersed Cr alloys for metallic interconnect of solid oxide fuel cell were prepared as a function of $LaCrO_3$ content in the range of 5 to 25 vol.% and were sintered at 1500$^{\circ}C$ under an Ar atmosphere with 5 vol.% $H_2$. The sintering and oxidation behaviors of these alloys were examined. The alloys indicated a good sinterability above 95% relative density at a given sintering condition, and their sintering densities is independent on $LaCrO_3$ content. The $LaCrO_3$ particles of the sintered alloys were concentrated on interfaces of Cr particles, and the size of the Cr particles increased with decreasing $LaCrO_3$ content, which is caused by inhibited grain growth of Cr particle by $LaCrO_3$ particle. The oxidation test showed all $LaCrO_3$-dispersed Cr alloys have good oxidation resistance as compared with pure Cr, which is attributed to presence of $LaCrO_3$ at the interface at which the oxidation reaction occurs rapidly. The Cr alloys with about 15 vol.% $LaCrO_3$ are very resistant to oxidation.

Structural and Dielectric Properties of $Pb(Mg_{1/3}Nb_{2/3})O_3$ Ceramics Substituted by Nd, La, K and Na (Nd, La, K, Na이 치환된 $Pb(Mg_{1/3}Nb_{2/3})O_3$ 세라믹의 구조 및 유전 성질에 관한 연구)

  • Kweon, Sook-Hwa;Park, Hyu-Bum;Kim, Jeong;Hong, Young-Sik;Kim, Si-Joong
    • Journal of the Korean Ceramic Society
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    • v.32 no.7
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    • pp.839-845
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    • 1995
  • The structural and dielectric properties of Pb(Mg1/3Nb2/3)O3 ceramics substituted by Nd3+, La3+, K+ and Na+ were studied over 0~50 at.% substituent content. The 1 : 1 ordering behavior of Mg2+ and Nb5+ ions in the B site sublattice was observed in Nd3+-and La3+-modified compounds. The degree of ordering was increased with Nd3+, La3+ content in the compounds. But K+-or Na+-modified compounds did not exhibit the ordering behavior. This was explained by charge and size effect of A and B site cations and oxygen vacancies. As the mole fractions of substituent increased, the maximum values of dielectric constants were rapidly decreased and the phase transitions were broadened. Phase transition temperature was correlated with the covalency of A-O and B-O bonding.

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