• Journal of the Korean Chemical Society
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• v.38 no.4
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• pp.276-282
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• 1994

Perovskite-type mixed oxides LaBO$_3$(B = Mn, Fe, Co) were prepared by citrate sol-gel method in $air(850^{\circ}C$, 24h). The oxygen stoichiometries and structures of these oxides were determined by XRD and TPR results as followings; LaMnO$_{3.16}$(a = 5.507, c = 13.329 $\AA$, hexagonal), LaFeO$_{3.17}$(a = 5.554, b = 5.555, c = 7.863 $\AA$, orthorhomibic), LaCoO$_{3.0}$(a = 5.436, c = 13.095 $\AA$, hexagonal). The temperature programmed reduction(TPR) experiments in static 300 torr H$_2$ atmosphere shows that the reduction reaction of LaBO$_3$(B = Mn, Fe, Co) proceeds into two stages, and thermal stabilities of these oxides decreased in the order of LaMnO$_3$ > LaFeO$_3$ > LaCoO$_3$. According to the kinetic analysis the lowest activation energy was obtained for LaCoO$_3$.

• The Journal of Natural Sciences
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• v.14 no.2
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• pp.41-54
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• 2004

$LaMnO_3$ and A site substituted $La_{0.9}Sr_{0.1}MnO_3$(a=$5.33\AA$, c=$13.27\AA$), B site substituted $LaMn_{0.9}Cu_{0.1}O_3$(a=$5.52\AA$, c=$13.31\AA$) mixed oxides were prepared by Citrate sol-gel method. The powder X-ray diffraction patterns of these oxides were indexed with single phase hexagonal perovskite structures. According to the TRR result, oxygen stoichiometry of these oxides were oxidative nonstoichiometry as like $LaMnO_{3.16}$, $La_{0.9}Sr_{0.1}MnO_{3.10}$ and $LaMn_{0.9}Cu_{0.1}O_{3.14}$ Reduction reactions of un-substituted $LaMnO_3$ was two steps, but specific site(A site of B site) partially substituted $LaMnO_3$ oxides were procees to three reactions.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3609-3614
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• 2013

Orthorhombic and hexagonal lanthanum(III) hydroxycarbonate ($LaCO_3OH$) and $Ln^{3+}$-doped $LaCO_3OH$ ($LaCO_3OH:Ln^{3+}$, where Ln = Ce, Eu, Tb, and Ho) powders were prepared by a hydrothermal reaction under ambient pressure and characterized by thermogravimetry, powder X-ray diffraction, infrared and luminescence spectroscopy, and field-emission scanning electron microscopy. The polymorph of $LaCO_3OH$ depended on the reaction temperature, inorganic salt additive, species of $Ln^{3+}$ dopant, and solvent. The calcination of orthorhombic $LaCO_3OH:Ln^{3+}$ (2 mol %) powers at $600^{\circ}C$ yielded a mixture of hexagonal and monoclinic $La_2O_2CO_3:Ln^{3+}$ powders. The relative quantity of the latter increased with decreasing ionic radius of the $Ln^{3+}$ dopant ion and increasing doping concentrations. On the other hand, the calcination of hexagonal $LaCO_3OH:Ln^{3+}$ (2 mol %) powders at $600^{\circ}C$ resulted in a pure hexagonal $La_2O_2CO_3:Ln^{3+}$ powder, regardless of the species of $Ln^{3+}$ ions (Ln = Ce, Eu, and Tb). The luminescence spectra of $LaCO_3OH:Ln^{3+}$ and $La_2O_2CO_3:Ln^{3+}$ were measured to examine the effect of their polymorph on the spectra.

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.718-722
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• 2017

We have investigated the photocatalytic activity for the decomposition of methyl orange on the pure $LaCoO_3$ and metal ion doped $LaCoO_3$ perovskite-typeoxides prepared using microwave process. In the case of pure $LaCoO_3$ and cesium ion doped $LaCoO_3$ catalysts, the formation of the perovskite crystalline phase was confirmed regardless of the preparation method. From the results of UV-Vis DRS, the pure $LaCoO_3$ and cesium ion doped $LaCoO_3$ catalysts have the similar absorption spectrum up to visible region. The chemisorbed oxygen plays an important role on the photocatalytic decomposition of methyl orange and the higher the contents of chemisorbed oxygen, the better performance of photocatalyst.

• 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.

• Journal of Surface Science and Engineering
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• v.29 no.6
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• pp.839-846
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• 1996

Epitaxial (La, Sr)$CoO_3/Pb(Zr,\;Ti)O_3/(La,\;Sr)CoO_3$by pulsed laser deposition for ferroelectric field effect transistor. Epitaxial $LaCoO_3/Pb(Zr,\;Ti)O_3/(La,\;Sr)CoO_3$ heterostructures exhibited 70$\mu C/cm^2$ and 17 $\mu C/cm^2$at a positively and negatively poled states, respectively. On the other hand, epitaxial (La, Sr)$CoO_3/Pb(Zr,\;Ti)O_3/LaCoO_3$heterostructures show the remnant polarization states opposite to the $LaCoO_3/Pb(Zr,\;Ti)O_3/(La,\;Sr)CoO_3$ heterostructures. This indicates that the interface between (La, Sr)$CoO_3$ (LSCO) and $Pb(Zr, Ti)O_3(PZT)$ layers affects the asymmetric polarization remanence through electrochemical nature. The resistivity of $LaCoO_3$ (LCO) layer was found to be dependent on an ambient oxygen, primarily the ambient oxygen pressure during deposition. The resistivity of the LCO layer varied in the range of 0.1-100 $\Omega$cm. It is suggested that, with an appropriate resistivity of the LCO layer, the LCO/PZT/LSCO heterostructure can be used as the ferroelectric field effect transistor.

• Journal of the Korean Chemical Society
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• v.36 no.5
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• pp.692-696
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• 1992

$NH_4^+ form cation exchange resin was used to separate one rare earth element from the rare earth mixture solution using Ln-EDTA eluent. Rare earth mixture solution was passed through the resin bed and eluted with 0.1M La-EDTA solution as an eluent. In here all the rare earth element except lanthanum ion are eluted and lanthanum ion absorbed in resin bed is eluted using 0.1M EDTA solution. If Ce-EDTA solution instead of La-EDTA solution was used as an eluent, all the rare earth element except cerium ion are eluted and cerium ion is eluted with 0.1M EDTA solution. This method can be applied to separate the individual rare earth element from the mixture. The separation mechanism is as follows: Absorption : 3RNH_4 ＋ Ln^{3+} = R_3Ln ＋ 3NH_4^+, La-EDTA elution : R_3Ln ＋ La-Y- = R_3La ＋ Ln-Y-, EDTA elution : R_3La ＋ HY^3- = La_-Y ＋ RH ＋ 2R^-.$

• 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.

• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.368-372
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• 1997

The microwave dielectric properties of (1-x)La2/3TiO3-xLaAlO3 system in which LaAlO3 having $\varepsilon$r$\geq$90 and positive $\tau$f was investigated. The crystal system of (1-x)La2/3TiO3-xLaAlO3 was pseudo-cubic in the range of 0.1$\leq$x$\leq$0.07. Its lattice constant increased with increasing x in spite that the amount of LaAlO3 containing of smaller Al(0.57 $\AA$) ion than Ti(0.64 $\AA$) increased. As the amount of LaAlO3 increased from x=0.1 to 0.9, the relative dielectric constant ($\varepsilon$r) decreased from 50 to 23 and the temperature coefficient of resonant frequency($\tau$f) decreased from +84 to -50. On the other hand, the value of Q.f0 reached a maximum (148,000 at 7 GHz) at x=0.7, where a rapid increase in the peak intensity of XRD occured, and further increased after prolonged sintering. The microwave dielectric properties of $\varepsilon$r=37, Q.f0=47,000 (at 7 GHz), and $\tau$f=-2 ppm/$^{\circ}C$ were obtained near 0.6La2/3TiO3-0.4LaAlO3 (x=0.4) composition.

• 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.