• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.2
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• pp.95-102
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• 2000

Methane combustion over perovskite-type oxides prepared using the malic acid method was investigated. To enhance the catalytic activity, the perovskite oxides were modified by the substitution of metal into their A or B site. In addition, the reaction conditions, such as the temperature, space velocity, and partial pressure of the methane were varied to understand their effect on the catalytic performance. With the LaCoO3-type catalyst, the partial substitution of Sr or Ba into site A enhanced the catalytic activity in the methane combustion. With the LaBO3(B=Co, Fe, Mn, Cu)-type catalyst, the catalytic activities were exhibited in the order of Co>Fe Mn>Cu. Futhermore, the partial substitution of Co into site B enhanced the catalytic activity, whereas an excess amount of Co decreased the activity. The surface area and catalytic activity of the perovskite catalysts prepared using the malic acid method showed higher values than those prepared using the solid reaction method. The catalytic activity was enhanced with decreased methane concentration and with a decrease in the space velocity.

• Journal of Magnetics
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• v.18 no.1
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• pp.30-33
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• 2013

The magnetocaloric effect and magnetization behavior have been analyzed in the double-perovskite $La_{0.7}Ba_{0.3}Mn_{1-X}Fe_XO_3$ compound with the sintering temperature at 1273 K. Samples were fabricated by the conventional solid-state reaction method. X-ray diffraction measurement revealed that all the samples had a single phase in orthorhombic. Detailed investigations of the magnetic entropy behavior of the samples were discussed with the variation of $T_C$. The magnetic entropy changes, ${\Delta}S_M$ of approximately 0.36-1.14 J/kg K were obtained in the temperature range of 145-350 K for the $La_{0.7}Ba_{0.3}Mn_{1-X}Fe_XO_3$ compound. The enhancement of the magnetic entropy change is believed to be due to changes in the microstructure, which changes the magnetic part of the entropy of a solid around the magnetic ordering temperature.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.803-810
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• 1998

We have studied the catalytic combustion of soot particulate 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, $O_2$ concentration, space velocity have been studied. The effect of $SO_2$ pretreatment and water introduced into reactants were also examined. In the $LaCoO_3$ catalyst, the partial substitution of alkali metals into A site enhanced the catalytic activity in the combustion of soot particulate and the activity was shown in the order : Cs>K>Na; In the $La_{0.6}Cs_{0.4}CoO_3 $; catalyst, the substitution of Fe or Mn showed no effect on the ignition temperature. The ignition temperature decreased with increasing $O_2$ concentration and contact time. The introduction of water into reactants feed decreased the ignition temperature and the pretreatment of $SO_2$ showed no effect on the catalytic activity.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.45.1-45.1
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• 2011

Cobalt-free $La_xSr_{4-x}Fe_6O_{13}$ ($0{\leq}x{\leq}2$) oxide have been synthesized and investigated as a potential cathode material for solid oxide fuel cells (SOFCs). $Sr_4Fe_6O_{13}$ consists of alternating perovskite layers ($Sr_4Fe_2O_8$) containing iron cations in octahedral oxygen coordination and $Fe_4O_5$ layers where iron cations have 5-fold coordination of two types-square pyramids and trigonal bipyramids. Our preliminary electrochemical testes of pristine $Sr_4Fe_6O_{13}$ show a rather high area specific resistance ($0.47{\Omega}cm^2$ at $700^{\circ}C$) for ~20 ${\mu}m$ thick layers with CGO electrolyte. The electrochemical performances are improved by La addition up to x=1 ($La_1Sr_3Fe_6O_{13}$, $0.06{\Omega}cm^2$ at $700^{\circ}C$). In addition, thermal expansion coefficient (TEC) values of $La_1Sr_3Fe_6O_{13}$ specimen demonstrated $15.1{\times}10^{-6}\;^{\circ}C^{-1}$ in the range of 25-900$^{\circ}C$, which provides good thermal expansion compatibility with the CGO electrolyte. An electrolyte supported (300-${\mu}m$-thick) single-cell configuration of $La_1Sr_3Fe_6O_{13}$/CGO/Ni-CGO delivered a maximum power density of 584 $mWcm^{-2}$ at $700^{\circ}C$. In addition, an anode supported single cell by YSZ electrolyte (10-${\mu}m$-thick) with a porous CGO interlayer between the cathode and the electrolyte to avoid undesired interfacial reactions exhibited 1,517 $mWcm^{-2}$ at $800^{\circ}C$. The unique composition of $La_1Sr_3Fe_6O_{13}$ with low thermal expansion coefficient and higher electrochemical properties could be a good cathode candidate for intermediate temperature SOFCs with CGO and YSZ electrolyte.

• Journal of the Korean Electrochemical Society
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• v.11 no.2
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• pp.89-94
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• 2008

We synthesized and investigated $(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$ perovskite oxides having different stoichiomety (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The electrochemical performances of the synthesized powders were investigated by AC impedance spectroscopy. Both the electric conductivity and the electrochemical performance showed the highest properties at the stoichiometry x = 0.02. Finally, we concluded that the variation of A-site deficiency results in the variation of the amount of oxygen vacancy and micro structure, which leads to the variation of electric conductivity and polarization resistance.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.162-168
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• 2006

The perovskites with nominal compositions $La_{0.8}Sr_{0.2}Fe_{1-x}M_xO_3$ (M=Co, Mn, Ni, x=0.1-0.3) were fabricated by a solid-state reaction method as cathode materials of low-temperature operating Solid Oxide Fuel Cells (SOFCs). X-ray diffraction analysis and microstructure observation for the sintered samples were performed. The ac complex impedance were measured in the temperature range $600-900^{\circ}C$ in air and fitted with a Solatron ZView program. The electrical conductivity and polarization resistance of $La_{0.8}Sr_{0.2}Fe_{1-x}M_xO_3$ (M=Co, Mn, Ni, x=0.1-0.3) were characterized systematically. The porosities of the sintered samples were in the range of 25% to 38%. The polarization resistance of $La_{0.8}Sr_{0.2}Fe_{0.7}M_{0.3}O_3$ was $0.291{\Omega}cm^2\;at\;700^{\circ}C$.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.21-26
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• 2000

Nanosized powders of trimetallic orthoferrites containing La and Sm in different ratios were synthesised by the thermal decomposition at low temperatures of the corresponding hexacyanocomplexes. The precursors and their decomposition products were analyzed by simultaneous thermogravimetric and differential thermal analysis (TG/DTA), x-ray diffraction (XRD) and Raman spectroscopy. Single phase trimetallic precursors and oxides were obtained. The crystal structure of the perovskitic oxides was orthorhombic, and the lattice parameters were affected by the ionic size of the rare earth elements present in the oxides. Raman spectroscopy showed a disorder effect in the vibrational bands with increasing the La content.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.994-1000
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• 2002

Oxygen permeability and the mechanical properties of mixed ionic-electronic conductive $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ perovskite-type membrane, fabricated by solid state reaction, were investigated with regard to microstructure. The microstructure of the membrane was controlled by changing the sintering temperature and holding time. The average grain size and relative density were evaluated as a function of sintering conditions. As the fraction of grain boundary decreased, oxygen permeability showed a tendency to increase. Especially the maximum oxygen flux of 0.37 ml/$cm^2$${\cdot}$min was measured for the specimen sintered at 1300${\circ}C$ for 10 h, which has high density and relatively large grain size. Fracture strength was dependent on the relative density of sintered body, while fracture toughness increased with average grain size.

• Journal of the Korean Magnetics Society
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• v.22 no.2
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• pp.37-41
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• 2012

The Ag nanoparticles attached $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$ (LSCF) perovskites were prepared by plasma method. The Ag nanoparticles with size of several nanometers deposited from the Ag target were coated on the surface of LSCF powders with size range from 0.2 to 3 ${\mu}m$. The agglomeration of Ag particles annealed at $800^{\circ}C$ under inert gas of Ar were rarely observed. The inter-diffusion between surface Ag and core LSCF is effectively strong to prevent aggregation of Ag nanoparticles. The wave number of FT-IR spectra for LSCF were largely shifted as the concentration of Ag on LSCF up to 2.11 wt.%. The ionic states of irons in LSCF were measured by M$\ddot{o}$ssbauer spectroscopy. The small amount of $Fe^{4+}$ ions are converted to $Fe^{3+}$ ions after Ag nanopartcles were coated on LSCF.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.102-103
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• 2002

LaMnO$_3$에 Ca을 치환한 Mn계 perovskite 구조(ABO3)의 물질에서 초거대자기저항 현상이 발견된 이후 R$_{1-x}$$^{3+}$ A$_{x}$$^{2+}$MnO$_3$(R=La, Nd, Pr: 희토류금속, A=Ca, Sr, Ba, Cd, Pb; 2가 양이온)계의 Mn 산화물의 연구가 고감도 자기 저항 센서와 자기기록 등의 활용가능성을 중심으로 활발히 진행되고 있다. 자기적 특성이 뛰어난 초거대자기저항물질에 대한 미시적인 자성에 대한 연구는 그 메커니즘이 복잡하고 다양한 접근방식에 따른다. (중략)