• Journal of the Korean Vacuum Society
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• v.17 no.2
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• pp.130-137
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• 2008

$La_{0.7}Sr_{0.3}MnO_3$ films were deposited on $SiO_2$/Si and Si substrates annealed at $350^{\circ}C$ by rf magnetron sputtering. The oxygen gas flow rates were varied as 0, 40, and 80 sccm. Without post annealing process, $La_{0.7}Sr_{0.3}MnO_3$ thin films on $SiO_2$/Si and Si substrates were polycrystalline with (100), (110), and (200) growth planes. The grain size of $La_{0.7}Sr_{0.3}MnO_3$ thin films was increased with increasing oxygen gas flow rate. The sheet resistance of $La_{0.7}Sr_{0.3}MnO_3$ thin films was decreased with oxygen flow rate due to the increased grain size which induced a reduction of grain boundary. TCR (temperature coefficient of resistance) values of $La_{0.7}Sr_{0.3}MnO_3$ thin films were obtained from -2.0% to -2.2%.

• Progress in Superconductivity
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• v.2 no.2
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• pp.71-75
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• 2001

The effect of annealing step-edges of LaAlO$_3$ and MgO single crystal substrates on YBa$_2$Cu$_3$O$_{7}$ junction has been studied. The step-edge was fabricated by argon ion milling and was annealed at 105$0^{\circ}C$ in 1 attn oxygen pressure. We compared AFM image near step-edge of the substrates between before and after annealing process. And YBa$_2$Cu$_3$O$_{7}$ thin film was deposited on the step-edge by a standard pulsed laser deposition. The step-edge junctions were characterized by current-voltage curves at 77 K. The annealing of step-edges of MgO substrate improved the current-voltage characteristic of Josephson junction: double steps in the current-voltage characteristic disappeared. However the annealing for LaAlO$_3$ did not improve the junction property.rty.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.6
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• pp.231-238
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• 2022

To secure the mechanical strength of porous Al₂O₃ ceramics, which can be utilized for filters and catalyst supports is essential for their functionality and durability. Superior mechanical strength would be obtained by tailoring the densification and grain growth during sintering. This study deals with grain growth behavior of a freeze-casted Al₂O₃ with addition of La₂O₃. In a temperature range between 1400 and 1600℃, variations of average grain size with sintering time and temperature were observed and analyzed with G_tⁿ-G₀ⁿ = kt and with k = k₀exp(-E_a/RT). As a result, n value and activation energy (E_a) for grain growth were calculated as 3 and 489.09 kJ/mol, respectively. These commonly confirms retardation effect of the La addition during sintering of Al₂O₃ porous structure. More accurate analysis on the La effect can be followed to provide useful guidance for the selection of additives for better mechanical strength in Al₂O₃ porous structures.

• Journal of Korean Vacuum Science & Technology
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• v.7 no.1
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• pp.8-12
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• 2003

The effects of lattice strain on the magnetic and the transport properties of La$_{0.8}$Sr$_{0.2}$MnO$_3$films grown on a LaAlO$_3$ (001) substrate and on a La$_{0.8}$Sr$_{0.2}$MnO$_3$ layer have been studied. It was observed that the metal-insulator and the ferromagnetic transitions turn out to be at higher temperatures for the film deposited on La$_{0.8}$Sr$_{0.2}$MnO$_3$ layer with respect to that on LaAlO$_3$. The dependence of Curie temperature on the bulk and the Jahn-Teller strains has also been determined. determined.

• Journal of Environmental Science International
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• v.13 no.7
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• pp.619-626
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• 2004

We have studied the catalytic combustion of soot particulates over perovskite-type oxides prepared by malic acid method, The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxide. In addition, the reaction conditions such as temperature and $O_2$ concentration were investigated. The partial substitution of alkali metals into A site in the $LaMnO_3$ catalyst, enhanced the catalytic activity in the combustion of carbon particulate and the activity was shown in the order: Cs > K > Na. For the $La_{1-x}Cs_{x}MnO_{3}$ catalysts, the catalytic activity showed the maximum value with x=0.3 but no more increase on the catalytic activity was shown with x > 0.3. For the $La_{0.8}Cs_{0.2}MnO_{3}$ catalyst, the substitution of Fe or Ni increased the ignition temperature. The ignition temperature decreased with an increase of $O_2$ concentration, however, no more increase in the catalytic activity was shown with $O_2$ concentration > 0.2. The introduction of NO into reactants showed no effect on the catalytic activity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.8
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• pp.616-619
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• 2012

Oxides possess several interesting properties, such as ferroelectricity, magnetism, superconductivity, and multiferroic behavior, which can effectively be used oxide electronics based on epitaxially grown heterostructures. The microscopic properties of oxide interfaces may have a strong impact on the electrical transport properties of these heterostructures. It was recently demonstrated that high electrical conductivity and mobility can be achieved in the system of an ultrathin $LaAlO_3$ film deposited on a $TiO_2$-terminated $SrTiO_3$ substrate, which was a remarkable result because the conducting layer was at the interface between two insulators. In this study, we observe that the current-voltage characteristics exhibit $LaAlO_3$ thickness dependence of electrical conductivity in $TiO_2$-terminated $SrTiO_3$. We find that the $LaAlO_3$ layers with a thickness of up 3 unit cells, result in highly insulating interfaces, whereas those with thickness of 4 unit cells and above result in conducting interfaces.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.505-511
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• 1997

The effects of sintering atmospheres(air, O2, N2) on the sintering and microwave dielectric properties of (1-x)CaTiO3-xLaAlO3 system was investigated. The sintered density of (1-x)CaTiO3-xLaAlO3 under air atmosphere increased linearly with increasing x, but it decreased in the range of x>0.5 under O2 atmosphere and x>0.6 under N2 atmosphere in spite of the increament of the smaller La(1.06$\AA$) and Al(0.5 $\AA$) ion than Ca(0.99$\AA$) and Ti(0.6$\AA$). In case of the air sintering atmosphere of (1-x)CaTiO3-xLaAlO3 the two phases of orthorhombic and rhombohedral crystal system were coexisting, and the XRD peak of rhombohedral crystalsystem was to be higher with increasing x. However, the sintering atmosphere of O2 and N2 made the monophasic crystal system of orthorhombic keep up by x=0.5 and x=0.6, respectively, and it transformed to pseudo-cubic crystal system in x>0.5 and x>0.6. The XRD peak intensity of (1-x)CaTiO3-xLaAlO3 was to be gradually higher with increasing x under the air atmosphere of sintering. Whereas, its XRD peak intensity increased till x=0.6 but decreased with increasing x in the range of x>0.6 under O2 and N2 atmosphere. The relative dielectric constant of (1-x)CaTiO3-xLaAlO3 sintered under air atmosphere decreased linearly and the Q.f0 value increased according as x increased. On the other hand, the relative dielectric constant of (1-x)CaTiO3-xLaAlO3 under O2 and N2 atmosphere decreased in the range of x$\leq$0.5 with increasing x, but increased rapidly in the range of x$\geq$0.6. And the Q.f0 value increased till x=0.6 but decreased in the range of x>0.6 with increasing x. The temperature coefficient of resonant frequency had no relation to sintering atmosphere.

• Bulletin of the Korean Chemical Society
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• v.22 no.3
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• pp.298-302
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• 2001

A site preference of niobium atom in Rb2-xLa2Ti3-xNbxO10 (0.0 $\leq$ x $\leq1.0)$ and RbLa2-xCaxTi2-xNb1+xO10 (0.0 $\leq$ x $\leq2.0)$, which are the solid-solutions between Rb2La2Ti3O10 and RbCa2Nb3O10, has been investigated by Raman spectroscopy. The Raman spectra of Rb2-xLa2Ti3-xNbxO10 (0.0 $\leq$ x $\leq1.0)$ gave an evidence that niobium atoms substituted for titanium atoms preferably occupy the highly distorted outer octahedral sites rather than the central ones in triple-octahedral perovskite layers. In contrast, the Raman spectra of RbLa2-xCaxTi2-xNb1+xO10 (0.0 $\leq$ x $\leq2.0)$ showed no clear information for the cationic arrangement in perovskite slabs. This difference indicated that a site preference of niobium atoms is observed only when the linear Rb-O-Ti linkage can be replaced by much stronger terminal Nb-O bond with double bond character. From comparison with the Raman spectroscopic behavior of CsLa2-xA’xTi2-xNb1+xO10 (A’ = Ca and Ba; 0.0 $\leqx\leq2.0)$, it is also proposed that a local difference in arrangement of interlayer atoms causes a significantly different solid acidity and photocatalytic activity of the layered perovskite oxides, despite their crystallographically similar structures.

• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1078-1084
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• 1998

lanthanum chromite(LaCrO3) powder was synthesized by the combustion of a solution of metal nitrates La(NO3).6H2O and Cr(NO3)3.9H2O and urea. The pH of solution affected a yield of the combustion products but did not influence the morphology of the products. When the pH of the solution was in the range of 0.7-4, the yield of the combustion products was more than 90% The morphology of the combustion products was af-fected by heating methods for the solution. The hot-plate induced heating of the solution yielded powders hav-ing two-dimensionally interconnected agglomerates whereas microwave-induced heating produced a fine and non-agglomerated powders. The specific surface area(BET) of the combustion products using microwave-in-non-agglomerated powders. The specific surface area(BET) of the combustion products using microwave-in-duced heating method were larger(25~32m2/g) than that of hot plate heating method(10-14m2/g)

• Korean Journal of Materials Research
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• v.11 no.6
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• pp.460-464
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• 2001

The ceramic diffusion coupling with the green body of calcium-doped lanthanum chromite(La$_{0.8}$Ca$_{0.2}$CrO$_3$CLC- G) and sintered calcium-doped lanthanum chromite(La$_{0.8}$Ca$_{0.2}$CrO$_3$ CLC) by Pechini's method on yttria stabilized zirconia(YSZ) plate has been investigated. The X-ray diffraction pattern of CLC sides at the reacted CLC-G/ CLC and CLC/YSZ interface were identified as La$_{1-x}$ Ca$_{x}$CrO$_3$ and the unreacted YSZ side was cubic-ZrO$_2$ at the treated condition, 1300~1500 C for 10 hr in air, respectively. The order of migration components between CLC/YSZ interface was Zr>La>>Cr>>>Ca and these changes were not dependent upon the treated conditions. The grain shape and size at the interface of CLC-G/CLC was appeared to have a uniform distribution with increasing temperature. The bonding reaction of YSZ/CLC was occurred without a large amount change of the compositions in SEM photos.os.otos.os.