• Journal of Magnetics
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• 제11권1호
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• pp.25-29
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• 2006

Recent experiments have demonstrated high TMR ratios in MTJs with the MgO barrier [1,2]. The CoFeB/MgO/CoFeB junctions showed better properties than the CoFe/MgO/CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB/MgO [3]. The amorphous CoFeB with 20 at%B starts the crystallization at $340^{\circ}C$ [4] and this crystallization of the CoFeB helps obtaining the high TMR ratio. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization were studied in annealed MTJs. XPS depth profiles were utilized. TEM analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B-oxide was formed at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization.

• 한국자기학회지
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• 제17권4호
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• pp.162-165
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• 2007

본 연구에서는 CoFeB/MgO/CoFeB 구조를 가지는 자기터널접합에서 capping층 재료의 종류와 열처리 시간에 따른 비정질 top CoFeB 자성층의 결정화 상태 및 자기터널접합의 자기적 특성 변화에 대한 연구결과를 비교 분석 하였다. Hcp(Hexagonal close-packed)의 결정구조를 가지는 Ru(002)를 capping층 재료로 사용한 자기터널접합 박막의 경우에는 열처리 이후 Ru과 인접한 부분의 top CoFeB이 bcc-CoFe(110)로 성장하는 반면, TiAl과 ZrAl을 capping층 재료로 사용한 자기터널접합의 경우는 열처리 이후 top CoFeB이 MgO와 epitaxial하게 bcc-CoFe(002)로 결정성장 하였다. 이로 인해 Ru을 사용한 자기터널접합의 터널자기 저항비(46.7%)보다 약 1.5배 높은 터널자기저항비(TiAl: 71.8%, ZrAl: 72.7%)를 나타내었다.

• 센서학회지
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• 제29권4호
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• pp.215-219
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• 2020

MnCo₂S₄/CoS₂ electrode with highly accessible electroactive sites is prepared using the hydrothermal method. The electrode exhibits an areal capacitance of 0.75 Fcm^-2 at 6 mAcm^-2 in 1 M KOH. The capacitance is further increased to 2.06 Fcm^-2 by adding K₃Fe(CN)₆ and K₄Fe(CN)₆ (a redox couple) to KOH. This increment is associated with the redox-active properties of cobalt and manganese transition metals, as well as the ion pair of [Fe(CN)₆]^-3/[Fe(CN)₆]^-4. The capacitance retention of the MnCo₂S₄/CoS₂ electrode is 87.5% for successive 4000 charge-discharge cycles at 10 mAcm^-2 in a composite electrolyte system of KOH and ferri/ferrocyanide. The capacitance enhancement is supported by the lowest equivalent series resistance (0.62 Ωcm^-2) of MnCo₂S₄/CoS₂ in the presence of redox additive couple compared with the bare KOH electrolyte.

• 한국세라믹학회지
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• 제53권3호
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• pp.306-311
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• 2016

Li-air batteries have received much attention due to their superior theoretical energy density. However, their sluggish kinetics on the cathode side is considered the main barrier to high performance. The rational design of electrode catalysts with high activity is therefore an important challenge. To solve this issue, we performed density functional theory (DFT) calculations to analyze the adsorption behavior of the $LiO_2$ molecule, which is considered to be a key intermediate in both the Li-oxygen reduction reaction (ORR) and the evolution reaction (OER). Specifically, to use the activity descriptor approach, the $LiO_2$ adsorption energy, which has previously been demonstrated to be a reliable descriptor of the cathode reaction in Li-air batteries, was calculated on $LaB_{1-x}B^{\prime}_xO_3$(001) (B, B' = Mn, Fe, Co, and Ni, x = 0.0, 0.5). Our fast screening results showed that $LaMnO_3$, $LaMn_{0.5}Fe_{0.5}O_3$, or $LaFeO_3$ would be good candidate catalysts. We believe that our results will provide a way to more efficiently develop new cathode materials for Li-air batteries.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 The 1st International Symposium on Advanced Magnetic Materials
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• pp.12.1-12.1
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• 2007

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제37회 하계학술대회 초록집
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• pp.254-254
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• 2009

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.61-64
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• 2008

$Pr_{0.3}Sr_{0.7}Co_{0.3}Fe_{0.7}O_{3-\delta}$ (PSCF3737) was prepared and characterized as a cathode material for intermediate temperature-operating solid oxide fuel cell (IT-SOFC). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and electrical property measurement were carried out to study cathode performance of the material. XPS and EXAFS results proved that oxygen vacancy concentration was decreased and lattice constants of the perovskite structure material were increased by doping Fe up to 70 mol% at B-site of the crystal structure, which also extended the distance between oxygen and neighbor atoms. Thermal expansion coefficient (TEC) of PSCF3737 is smaller than that of $Pr_{0.3}Sr_{0.7}CoO_{3-\delta}$(PSC37) due to lower oxygen vacancy concentration. PSCF3737 showed better cathode performance than PSC37. It might be due good adhesion by a smaller difference of TEC between $Gd_{0.1}Ce_{0.9}O_2$ (CGO91) and electrode. Composite material PSCF3737-CGO91 showed better compatibility of TEC than PSCF3737. However, PSCF3737-CGO91 did not represent higher electrochemical property than PSCF3737 due to decreased reaction sites by CGO91.

• Bulletin of the Korean Chemical Society
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• 제14권4호
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• pp.439-444
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• 1993

The aerobic oxidation of the Fe(II) complex of 1,4,8,11-tetraazacyclotetradecane, [Fe(cyclam)$(CH_3CN)_2](ClO_4)_2$, in MeCN in the presence of a few drops of $HClO_4$ leads to low spin Fe(III) species [Fe(cyclam)$(CH_3CN)_2](ClO_4)_3$. The Fe(III) cyclam complex is further oxidized in the air in the presence of a trace of water to produce the deep green binuclear bismacrocyclic Fe(II) complex $[Fe_2(C_{20}H_{36}N_8)(CH_3CN)_4](ClO_4)_4{\cdot}2CH_3CN$. The Fe(II) ions of the complex are six-coordinated and the bismacrocyclic ligand is extensively unsaturated. $[Fe_2(C_{20}H_{36}N_8)(CH_3CN)_4](ClO_4)_4{\cdot}2CH_3CN$ crystallizes in the monoclinic space group $P2_1/n$ with a= 13.099 (1) ${\AA}$, b= 10.930 (1) ${\AA}$, c= 17.859 (1) ${\AA}$, ${\beta}$= 95.315 $(7)^{\circ}$, and Z= 2. The structure was solved by heavy atom methods and refined anisotropically to R values of R= 0.0633 and $R_w$= 0.0702 for 1819 observed reflections with F > $4{\sigma}$ (F) measured with Mo K${\alpha}$ radiation on a CAD-4 diffractometer. The two macrocyclic units are coupled through the bridgehead carbons of ${\beta}$-diimitie moieties by a double bond. The double bonds in each macrocycle unit are localized. The average bond distances of $Fe(II)-N_{imine}$, $Fe(II)-N_{amine}$, and $Fe(II)-N_{MeCN}$ are 1.890 (5), 2.001 (5), and 1.925 (6) ${\AA}$, respectively. The complex is diamagnetic, containing two low spin Fe(II) ions in the molecule. The complex shows extremely intense charge transfer band in the near infrared at 868 nm with ${\varepsilon}$= 25,000 $M^{-1}cm^{-1}$. The complex shows a one-electron oxidation wave at +0.83 volts and two one-electron reduction waves at -0.43 and-0.72 volts vs. Ag/AgCl reference electrode. The complex reacts with carbon monoxide in $MeNO_2$ to form carbonyl adducts, whose $v_{CO}$ value (2010 $cm^{-1}$) indicates the ${\pi}$-accepting property of the present bismacrocyclic ligand.