• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.59-64
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• 2003

We fabricated mixed ionic-electronic conducting membranes, $CH_4\;Using\;{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, by solid state reaction method for solid oxide fuel cell. The membranes consisted of single perovskite phase and exhibited high relative density, $>95\%$. We coated $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ layer using screen printing method in order to improve surface reactivity of the $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$. As a result, the oxygen permeation flux of the coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ showed higher value, $0.5ml/min{\cdot}cm^2\;at\;950^{\circ}C$ than the uncoated one. Higher oxygen permeation was observed in the porously coated Lao $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$membranes with larger grain sizes. Syngas, $CO+H_2$, was successfully obtained from methane gas, $CH_4$, using the $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, with over $40\%\;of\;CH_4$ conversion and syngas yield. $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ membrane was stable even when it was exposed to the reducing environment, methane, for 600 hrs at $950^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1991.10a
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• pp.37-39
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• 1991

This paper is studies the effects of additives on the magnetic properties of Sr-ferrite. The specimens have been composed of SrO and Fe$_2$O$_3$with ratio of 1:5.9. As 1st additives, it is mixed to 0.2wt%, 0.7wt% and 1wt% of CaCo$_3$with 0.3wt% SiO$_2$. As 2nd addition, it is mixed to 0.5wt%, 1wt% of Na$_2$SiO$_3$, 0.5wt%, 1wt% of Cr$_2$O$_3$and 0.5wt%, 1wt% of Al$_2$O$_3$and sintering conditions was carried out at 1210$^{\circ}C$, 1230$^{\circ}C$ and 1250$^{\circ}C$. From experiments on the magnetic properties of specimen, the results were shown follows; (1) In case of additive SiO$_2$and CaO, it is stable magnetoplumbite structure for liquid phase grown, enhances mignetic propertics. (2) In case of basic compositions + 0.5wt% Al$_2$O$_3$, it is confirmed better properties by increasing of the coercivity than 0.5wt% Cr$_2$O$_3$additives. (3) In case of mixed additives of Cr$_2$O$_3$and Al$_2$O$_3$, magnetic propeties decrease with sintering density.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.133-136
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• 2007

Perovskite-structured samarium strontium cobaltite (SSC), which is mixed ionic electronic conductor (MIEC), is considered as a promising cathode material for intermediate temperature-operating solid oxide fuel cell (SOFC) due to its high electrocatalytic property. Cathode material containing cobalt (Co) is unstable at high temperature and has a relatively high thermal expansion property. In this paper, Sm-Sr-(Co,Fe,Ni)-O system with perovskite and spinel structures was investigated in terms of electrochemical property and thermal expansion property, respectively. Area specific resistance (ASR) was measured by ac impedance spectroscopy to investigate the electrochemical property of cathode, and thermal expansion coefficient (TEC) was measured by using dilatometer. Micro structure of cathode was observed by scanning electron microscopy. Perovskite-structured $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$ showed the ASR of $0.87{\Omega}/cm^{2}$, and $Sm_{0.5}Sr_{0.5}NiO_{3-\delta}$, which actually has a spinel structure, showed the lowest TEC value of $13.3{\times}10^{-6}/K$.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.477-483
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• 2008

$La_{0.7}Sr_{0.3}Co_{0.2}Fe_{0.8}O_{3-{\delta}$ oxide was synthesized by a citrate method and a typical dense membrane of perovskite oxide has been prepared using as-prepared powder by pressing and sintering at $1300^{\circ}C$. Precursor of $La_{0.7}Sr_{0.3}Co_{0.2}Fe_{0.8}O_{3-{\delta}$ prepared by citrate method was investigated by TGA and XRD. Metal-citrate complex in precursor was decomposed into perovskite oxide in the temperature range of $260{\sim}410^{\circ}C$ but XRD results showed $SrCO_3$ existed as impurity at less than $900^{\circ}C$. Electrical conductivity of membrane increased with increasing temperature but then decreased over $700^{\circ}C$ in air atmosphere ($Po_2=0.2atm$) and $600^{\circ}C$ in He atmosphere ($Po_2=0.01atm$) respectively due to oxygen loss from the crystal lattice. The oxygen permeation flux increased with increasing temperature and maximum oxygen permeation flux of $La_{0.7}Sr_{0.3}Co_{0.2}Fe_{0.8}O_{3-{\delta}$ membrane with 1.6 mm thickness was about $0.31cm^3/cm^2{\cdot}min$ at $950^{\circ}C$. The activation energy for oxygen permeation was 88.4 kJ/mol in the temperature range of $750{\sim}950^{\circ}C$. Perovskite structure of membrane was not changed after permeation test of 40 h and the membrane was stable without secondary phase change with 0.3 mol Sr addition.

• Electrical & Electronic Materials
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• v.5 no.3
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• pp.329-336
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• 1992

본 논문은 이방성 Sr.페라이트의 자기특성의 개선에 관하여 연구한 것이다. 시편은 SrO.nFe$_{2}$O$_{3}$의 기본조성으로서 비화학양론적 영역인 n=5.9를 택하였다. 그리고 보자력을 증가시키기 위하여 기본첨가제로서 0.7wt% CaCO$_{3}$와 0.3% wt% SiO$_{2}$를 첨가하여 하소시킨 다음 $Na_{2}$SiO$_{3}$의 량을 변화시키면서 복합첨가하였다. 한편, 위의 시료(기본첨가제와 0.5wt% $Na_{2}$SiO$_{3}$)에 Cr$_{2}$O$_{3}$ 및 $Al_{2}$O$_{3}$를 단독 및 복합첨가한 결과, 0.5wt% $Al_{2}$O$_{3}$가 단독첨가되었을 경우, 좋은 자기특성을 나타내었다. 본 연구에서 시행한 복합첨가방식에 의한 Sr.페라이트의 자기특성의 조사를 통하여 등방성의 경우, 기본조성과 기본첨가제와 0.5wt% $Na_{2}$SiO$_{3}$와 0.5wt% $Al_{2}$O$_{3}$조성에서 (BH)$_{max}$=1.15MGOe, 그리고 이방성의 경우, (BH)$_{max}$=3.23MGOe를 얻었으며 시료를 이방성화하므로서 자기특성면에서 등방성인 경우의 2~3배의 개선효과를 얻었다. 그리고 소결온도는 1210.deg.C에서 가장 좋은 특성을 나타내었으며 큐리온도는 등방성의 경우 T$_{c}$=410~420.deg.C에서 이방성의 경우 T$_{c}$=439~445.deg.C로서 약 30.deg.C가 향상되었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.120-123
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• 1997

In this paper, we deal with the effect on magnetic properties when Nd is added to Sr ferrite bonded magnet. First, we choose SrO$_{n}$.Fe$_2$O$_3$(n=5.9), which is nonstoichiomatric composition, as specimen ferrite. Then, we add 5wt% polyvinyl alcohol and calcinate at 12$25^{\circ}C$ under $N_2$ environment for carbon coating on chemical compound specimen. After that we obtain 1.2${\mu}{\textrm}{m}$ single domain powder through grinding process for 18 hours. The single domain Sr ferrite Powder is well mixed with silage coupling and calcium stearate of 1wt% Then, it is kneaded by using polyamide12 as a binder and is pelleted. After adding Nd-Fe-B powder to the pelleted specimen, we injection-mould it under magnetic field by using anisotropic mould. Especially, when we add l3wt% Nd-Fe-B powder to the polyamide12, we obtain excellent magnetic propertiecs which are $_{B}$H$_{C}$=2.65KOe, Br=3.16KG and (BH)$_{max}$=2.61MGOeOeOeOeOe

• Journal of the Korean Magnetics Society
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• v.14 no.2
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• pp.76-82
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• 2004

Crystallographic and magnetic properties for Brownmillerite-type oxides $Ca_{1-x}$Sr$_{x}$FeO$_{2.5}$ (x = 0, 0.3, 0.5, 0.7, 1.0) were investigated using x-ray diffraction (XRD) and Mossbauer spectroscopy. Polycrystalline samples were prepared by conventional solid-state reaction method. Information on exact crystalline structures, lattice parameters, bond lengths and bond angles were obtained by refining their XRD profiles using a Rietveld method. The crystal structures were found to be all orthorhombic with space group Icmm (x = 0, 0.3) and Icmm (x = 0.5, 0.7, 1.0) The lattice parameters increased monotonically with increasing Sr concentration. Both the tetrahedral and the octahedral sites were considerably distorted and elongated along b-axis. While bond lengths and bond angles O-Fe-O tend to increase minutely with the increase of Sr content, bond angles Fe-O-Fe decreased accordingly. The Mossbauer spectra showed two sets of sharp sextets originating from ferric ions occupying the tetrahedral and the octahedral sites under the magnetic transition temperature T$_{N}$. Regardless of the compositions x, the electric quadrupole splittings were -0.3 mm/s and 0.4 mm/s for the octahedral and the tetrahedral site, respectively. Above T$_{N}$, the Mossbauer spectra showed the paramagnetic doublets whose electric quadrupole splittings were about 1.6 mm/s, irrespective of compositions x. T$_{N}$ was found to decrease monotonically with the increase of Sr concentration. Ratios of absorption area for the two sites were almost 1:1 up to as high as 0.95 T$_{N}$ for all x. The result of the Debye temperature indicated that the inter-atomic binding force for the Fe atoms in the tetrahedral site was stronger than that for the octahedral site.hedral site.

• Journal of Powder Materials
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• v.13 no.2 s.55
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• pp.112-118
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• 2006

[ $R_{1/3}Sr_{2/3}FeO_{3}$ ](R=Pr, Nd, and Sm) was synthesized and their magnetic properties and charge ordering(CO) transition related with lattice dynamics and oxygen vacancy were systematically investigated. The charge disproportion ation(CD) in $R_{1/3}Sr_{2/3}FeO_{3}$(R=Pr,Nd) was in which two kins of iron with valence state $Fe^{3+}$ and $Fe^{5+}$ were found with ratio of 2:1. In this charge ordering state a sequence of $Fe^{3+}Fe^{3+}Fe^{5+}Fe^{3+}Fe^{3+}Fe^{5+}$ exists aligned along the [111] direction of the pseudocubic perovskite structure. The charge ordering exist in distorted structure involving $t_{pd}$ hybridization. The disordering phases coexist in distorted structure as temprature in creases that is controlled amount of oxygen vacancy. The magnetic hyperfine fields indicate charge tranfering temperature as it dissapeared drastically.

• The Journal of the Petrological Society of Korea
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• v.12 no.3
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• pp.119-134
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• 2003

Yuksipryeong two-mica granite presents strongly peraluminous characteristics in both mineralogy and geochemistry. It has high aluminum saturation index with 1.15∼l.20 and high corundum with 2.20∼2.98 wt% CIPW norm. As the color index is <16% and FeO$\^$T/+ MgO + TiO$_2$is average 1.9 wt％, it corresponds to leucogranite. Yuksipryeong two-mica leucogranite shows negative linear trend for TiO$_2$, Al$_2$O$_3$, FeO, Fe$_2$O$_3$, MgO, CaO, K$_2$O, P$_2$O$\_$5/, Rb, Ba, and Sr as SiO$_2$increases, and the positive relation of Zr and Th, which result from feldspar, biotite, apatite and zircon fractionation. Pegmatitic dike has higher SiO$_2$and P$_2$O$\_$5/, but lower another major elements. Yuksipryeong two-mica leucogranite has lower Rb, but higher Ba and Sr than Manaslu, Hercynian two-mica leucogranites, and S-type granites in Lachlan Fold Belt. Pegmatitic dike has higher Rb and Nb but lower Ba, Sr, Zr, Th, and Pb contents than Yuksipryeong two-mica leucogranite, resulting in removing or mobilizing for some trace elements from the granitic melt. Yuksipryeong two-mica leucogranite has total REEs with 95.7∼l23.3 ppm, and chondrite-normalized REE pattern is very steep ((La/Yb)$\_$N/ = 6.9∼24.8), light REEs (LREEs)-enriched End heavy REEs (HREEs)- depleted pattern with low to moderate Eu anomalies (Eu/Eu＊= 0.7∼0.9). While pegmatitic dike has low total REEs with 7.0 ppm, and chondrite-normalized REE pattern is flat-pattern ((La/Yb)$\_$N/ = 2.1) with strong negative Eu anomalies (Eu/Eu＊= 0.2). The melt compositions having formed two-mica leucogranites depend on not only the source rock but also the amounts of the residual remaining after melting of source rocks. The CaO/Na$_2$O and Rb/Sr-Rb/Ba ratios depend mainly on the composition of source rocks in the strongly peraluminous granite, that is, plagioclase/clay ratio of the source rocks. Yuksipryeong two-mica leucogranite has higher CaO/Na$_2$O and lower Rb/Sr-Rb/Ba ratios than Manaslu and Hercynian two-mica leucogranites (Millevaches and Gueret) derived from clay-rich, plagioclase-poor (polite), which suggest that the probable source rocks for Yuksipryeong two-mica leucogranite is clay-poor, plagioclase-rich quartzofeldspathic rocks. As the concentrations of Al$_2$O$_3$remain nearly constant but those of TiO$_2$increases as increasing temperature in the strong peraluminous melt, the Al$_2$O$_3$/TiO$_2$ratio may reflect relative temperature at which the melts have formed. Comparing the polite-derived Manaslu and Hercynian two- mica leucogranites, Manaslu two-mica leucogranite has higher Al$_2$O$_3$/TiO$_2$ratio than latter, and its melt have formed at relatively lower temperature ($\leq$ 875$^{\circ}C$) than Hercynian two-mica leucogranites. Likewise, comparing the quartzofeldspathic rock-derived granites, Yuksipryeong two-mica granite has higher Al$_2$O$_3$/TiO$_2$, ratio than S-type granites in Lachlan Fold Belt (>875$^{\circ}C$). The melt formed Yuksipryeong two-mica leucogranite are considered to have been formed at temperature at below the maximum 875$^{\circ}C$C$.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.86-87
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• 2002

Fe과 Mo이 교대로 정렬해 있는 이중 페로브스카이트 구조를 갖는 $A_{2-x}$FeMo $O_{6}$(A=Ca, Sr, Ba) 화합물들은 망간 산화물들에 비해 높은 $T_{c}$ (310-420K)의 준강자성 상태를 갖는다.$^{1.3}$ 이 화합물들은 F $e^{3+}$ (S=5/2) 와 M $o^{5+}$(S=1/2) 스핀들 사이의 커다란 반강자성 상호작용으로 이론적으로 4$\mu$$_{B}$/f.u.의 $M_{s}$ 값을 갖는다. A-site의 평균 이온 반경( $r_{A}$)이 증가함에 따라 이 화합물들의 결정구조는 Monoclinic(A=Ca)에서 Tetragonal(Sr)과 Cubic(Ba)으로 점진적으로 변화한다.$^3$(중략)(중략)략)략)