• 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.

• Bulletin of the Korean Chemical Society
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• v.27 no.11
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• pp.1839-1843
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• 2006

Hydrothermal reactions of $Ln(NO_3)_3{\cdot}5H_2O $ (Ln = Eu (1), Sm (2), Ho (3), Dy (4)) with 3,5-pyridinedicarboxylic acid (3,5-pdcH2) in the presence of 4,4'-bipyridine led to the formation of the 3-D Ln(III)-coordination polymers with a formula unit of $[Ln_2(3,5-pdc)_2(C_2O_4)(H_2O)_4]{\cdot}2H_2O$. These polymers contain a bridging oxalate ligand ($C_2O_4\;^2$). On the basis of GCMS study of the mother liquor remaining after the reaction, we proposed that the $C_2O_4\;^2$ formation proceeds in three steps: (1) Ln(III)-mediated decarboxylation of $3,5-pdcH_2$ to give $CO_2$, (2) the reduction of $CO_2$ to $CO_2\;^{\cdot}$ by the Ln(II) species, and (3) the reductive coupling of the two $CO_2\;^{\cdot}$ radicals to the oxalate ($C_2O_4\;^2$) ion. All polymers were structurally characterized by X-ray diffraction.

• Bulletin of the Korean Chemical Society
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• v.17 no.2
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• pp.168-172
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• 1996

The variations of the structural detail of layered perovskite-type oxides, Na2Ln2Ti3O10 (Ln=La, Nd, Sm, Gd), have been refined by Rietveld analyses of their powder X-ray diffraction data. Although the c-axis strongly decreases from Ln=La to Nd, Sm, or Gd, the length of Na-O bond along the c-axis that is regarded as the sodium layer spacing is not dependent on the unit cell parameter. Such a behavior is explained by the fact that Na-O bond is in competition with Ti-O one of the perovskite slab. Increased covalency of this Ti-O bond by the lattice contraction leads to weakening of the attaching strength of Na ion. This picture is consistent with the experimental observation that Na ion conductivity of Na2Ln2Ti3O10 increases from Ln=La to Nd, Sm, or Gd despite strong contraction of the unit cell volume.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1116-1117
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• 2006

Lanthanide tantalite $LnTaO_4$ (Ln= La, Nd, Sm, Dy, Er and Tm) was synthesized by a solid state reaction between mixed powders of $Ln_2O_3$ and $Ta_2O_5$. The single-phase $LnTaO_4$ was prepared by sintering at temperatures of 1423-1673 K in air. The SEM observation showed that the particles were provided with the growth steps and the depeloped facets. The photocatalytic activity for water splitting of $LnTaO_4$ prepared was measured under UV light irradiation. The activity obtained was higher than that previously reported. These results suggested the crystallinity of $LnTaO_4$ photocatalysts correlates closely with the efficiency of water splitting.

• Journal of the Korean Chemical Society
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• v.43 no.6
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• pp.628-635
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• 1999

Direct preparative method of 2,6-diformyl-p-cresol and 2-hydroxy-3-hydroxy-5-methylbenzaldehyde from 2,6-bis(hydroxymethyl)-4-methylphenol using activated $Mn(IV)O_2$ was described. Hexadentate compartmental Iigands, $H_4L[A]\;and\; H_4L[B]$ were prepared by condensation reactions of 2-hydroxy-3-hydroxy methyl-5-methylbenzaldehyde with ethylenediamine and 1,3-diaminopropane respectively. By the reaction of macrocycle($H_4[20]DOTA$) with Ln(III) nitrate {Ln(III)=Pr, Sm, Cd, Dy }, discrete mononuclear Ln(III) complexes of the type $[Ln(H_2[20]DOTA)(ClO_4)(H_2O)]\;{\cdot}\;3H_2O$ were synthesized in the solid state. $[Ln([20]DOTA)(NO_3)(H_2O)](NO_3)_2\;{\cdot}\;xH_2O$ was placed in methanol for 2 days, and $[Ln([20]DOTA)(NO_3)(CH_3OH)]^{2+}$ was formed. The equilibrium constants(K) for the substitution of coordinated $CH_3OH$ in the Ln-[20]DOTA complexes by various auxiliary ligand, $L_a$(=salicylic acid, p-chlorobenzoic acid, benzoic acid, acetic acid, 4-bromophenol) were determined spectroscopically at 25$^{\circ}C$ and 0.1M $NaClO_4$. The K values calculated were in the order of salicylic acid > p-chlorobenzoic acid > benzoic acid > acetic acid > 4-bromophenol, while pKa of auxiliary ligands was in the opposite trend.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.233-236
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• 2009

In this study, the characteristic of the hybrid rocket motor with $LN_2O$(Liquid Nitrous oxide) was investigated experimentally. HDPE(High Density PolyEthlene) was used as fuel with different sized single port. When used $LN_2O$, combustion efficiency is lower than using $GN_2O$(Gas Nitrous oxide), because of completeness of vaporization of droplet and mixing. And regression rate was changed by different oxidizer phase. This behavior was considered that flame temperature and combustion of solid fuel front/end surface.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3420-3424
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• 2013

The reaction of $LnCl_3{\cdot}7H_2O$ [Ln = La (1), Ce (2)] with salicylic acid (HL) and 1,10-phenanthroline (Phen) at $20^{\circ}C$ in $H_2O$/ethanol gave after work-up and recrystallization two novel lanthanide complexes with general formula $[Ln(Phen)_2(L)_3(HL)]{\cdot}H_2O$. Compounds 1 and 2 were characterized by IR and UV-Vis spectroscopy, TGA, CHN as well as by X-ray analysis. According to these results, compounds 1 and 2 are isostructural and contain $Ln^{3+}$ ions with coordination number nine. Complexes 1 and 2 consist of two Phen, one neutral HL and three L anions (two L anions act as monodentate ligands and the third one is chelating to $Ln^{3+}$). Thermal decomposition led to primary loss of the Phen molecules. Then HL molecules and finally L moieties left the material to give $Ln_2O_3$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.337-340
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• 1999

Since the first reports of CMR(colossal magnetoresistance) effects in some single crystal R-P Phase Ln$_{1-x}$ Sr$_{2-x}$Mn$_{2}$O$_{7}$ 1996. many researches have been carried out to find optimum compositions and processing conditions in this system. In this study, layered perovskite R-P Phase Ln$_{1-x}$ Sr$_{2-x}$Mn$_{2}$O$_{7}$ (x=0.4, Ln=-La, Eu, Gd, Nd, Pr, Sm) phases were synthesized by solid state reaction and their structures were refined by Rietveld method. Electrical and magnetic properties were measured drown to 20K and compare with those of R-P Phase Ln$_{1-x}$ Sr$_{2-x}$Mn$_{2}$O$_{7}$ Phases.es.es.es.es.es.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.726-729
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• 2000

Though L $a_{1+x}$S $r_{2-x}$M $n_2$ $O_{7}$ n=2 R-P phases have been well known to have CMR effect, it was generally believed that n=1 phase was insulating. But recently monolayered perovskite $Ca_{2-x}$L $n_{x}$Mn $O_4$phase has been reported to show magnetoresistance. In this study, layered perovskite $Ca_{2-x}$L $n_{x}$Mn $O_4$ (x=0, 0.5, Ln=Pr, Nd, Sm, Gd) phases were synthesized by solid state reaction and their structures were refined by Rietveld method. The space groups of $Ca_2$Mn $O_4$, N $d_{0.5}$C $a_{1.5}$Mn $O_4$phases were refined as C2cb and Fmmm, respectively.y.ely.y.y.y.y.y.y.