• 한국자기학회:학술대회 개요집
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• 한국자기학회 1998년도 추계연구발표회 논문개요집
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• pp.64-65
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• 1998

• Journal of Magnetics
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• 제20권1호
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• pp.26-30
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• 2015

The crystallographic and magnetic properties of gallium-substituted cobalt ferrite ($CoGa_xFe_{2-x}O_4$) were investigated. The new material was synthesized using conventional ceramic methods, with gallium substituted for ferrite in the range of x = 0.0 to 1.0, in steps of 0.2. X-ray diffraction and M$\ddot{o}$ssbauer spectroscopy were used to confirm the presence of crystallized particles in the $CoGa_xFe_{2-x}O_4$ ferrite powders. All of the samples exhibited a single phase with a spinel structure, and the lattice parameters decreased as the gallium content increased. The particle size of the samples also decreased as gallium increased. For $x{\leq}0.4$, the M$\ddot{o}$ssbauer spectra of $CoGa_xFe_{2-x}O_4$ could be fitted with two Zeeman sextets, which are the typical spinel ferrite spectra of $Fe^{3+}$ with A- and B-sites. However, for $x{\geq}0.6$, the M$\ddot{o}$ssbauer spectra could be fitted with two Zeeman sextets and one doublet. The variation in the M$\ddot{o}$ssbauer parameters and the absorption area ratio indicated a cation distribution of $(Co_{0.2-0.2x}Ga_xFe_{0.8-0.6x})[Co_{0.8+0.2x}Fe_{1.2-0.4x}]O_4$, and the magnetic behavior of the samples suggested that the increase in gallium content led to a decrease in the saturation magnetization and in the coercivity.

• 센서학회지
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• 제18권3호
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• pp.234-238
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• 2009

We have investigated the effects of dopant on the thermoelectric properties that $La_{(1-x)}M_xCoO_3$(M=Sr, Ca;x=0, 0.1) bulk ceramics fabricated by the conventional solid state reaction method. The Seebeck coefficient of $La_{(1-x)}M_xCoO_3$(M=Sr, Ca;x=0, 0.1) bulk ceramics was measured at wide temperature range from 300 K to 673 K. The thermoelectric properties(Seebeck coefficient and electrical resistivity) depend strongly on the kinds of dopants. Sr and Ca dopant decrease the Seebeck coefficient. Density of sintered $La_{0.9}Sr_{0.1}CoO_3$ ceramic at 1523 K was 7.12 $g/cm^2$ and Seebeck coefficient was 35 ${\mu}V/K$ at 663 K. However, the electrical resistivity of the Sr doped sample was low and stable.

• Bulletin of the Korean Chemical Society
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• 제7권2호
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• pp.102-105
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• 1986

Samples with the nominal composition of $Co_{9-x}M_xS_8$(M = Ni, Rh, Ru, and Fe) were prepared, and their magnetic properties were measured. X-ray diffraction analysis showed that small amount of the elements Ni, Rh, and Fe could be incorporated into $Co_9S_8$ forming a homogeneous ${\pi}$-phase, whereas the Ru-incorporated sample could not be prepared in a single phase. The lattice parameter was observed to increase as other elements were incorporated into $Co_9S_8$. Samples incorporated with the elements of Ni, Rh, and Ru showed Pauli-paramagnetism while the Fe-incorporated sample exhibited weak ferromagnetism. The values of magnetic susceptibility for the Ni, Rh, Ru-incorporated samples were nearly the same as that of pure $Co_9S_8$.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.16-16
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• 2002

The presently commercialized lithium-ion batteries use layer structured LiCoO₂ cathodes. Because of the high cost and toxicity of cobalt, an intensive search for new cathode materials has been underway in recent years. Recently, a concept of a one-to-one solid state mixture of LiNO₂ and LiMnO₂, i.e., Li[Ni/sub 0.5/Mn/sub 0.5/]O₂, was adopted by Ohzuku and Makimura to overcome the disadvantage of LiNiO₂ and LiMnO₂. Li[Ni/sub 0.5/Mn/sub 0.5/]O₂ has the -NaFeO₂ structure, which is characteristic of the layered LiCoO₂ and LiNiO₂ structures and shows excellent cycleability with no indication of spinel formation during electrochemical cycling. Layered Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials with high homogeneity and crystallinity were synthesized using a mechanical alloying method. The Li[Ni/sub 0.475/Co/sub 0.05/Mn/sub 0.475/]O₂ electrode delivers a high discharge capacity of 187 mAh/g between 2.8 and 4.6 V at a high current density of 0.3 mA/㎠(30 mA/g) with excellent cycleability. The charge/discharge and differential capacity vs. voltage studies of the Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials showed only one redox peak up to 50 cycles, which indicates that structural phase transitions are not occurred during electrochemical cycling. The magnitude of the diffusion coefficients of lithium ions for Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂(x = 0.5 and 0.475) are around 10/sup -9/ ㎠/s measured by the galvanostatic intermittent titration technique (GITT).

• Journal of Magnetics
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• 제11권1호
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• pp.51-54
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• 2006

Variation of magnetic properties through Cr substitution for Co in inverse-spinel $CoFe_2O_4$ has been investigated by vibrating-sample magnetometry (VSM) and conversion electron $M\ddot{o}ssbauer$ spectroscopy (CEMS). $Cr_{x}Co_{1-x}Fe_2O_4$ samples were prepared as thin films by a sol-gel method. The lattice constant of the $Cr_{x}Co_{1-x}Fe_2O_4$ samples was found to remain unchanged, explainable in terms of a reduction of tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$ due to substitution of $Cr^{3+}$ ion into octahedral $Co^{2+}$ site. The existence of the tetrahedral $Fe^{2+}$ ions in $Cr_{x}Co_{1-x}Fe_2O_4$ was confirmed by CEMS analysis. Room-temperature magnetic hysteresis curves for the $Cr_{x}Co_{1-x}Fe_2O_4$ films measured by VSM revealed that the saturation magnetization $M_s$ increases by Cr doping. The $M_s$ is maximized when x = 0.1 and decreases for higher x but is still bigger than that of $CoFe_2O_4$. The increase of $M_s$ can be explained partly by the reduction of the tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$.

• 한국안광학회지
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• 제3권1호
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• pp.223-228
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• 1998

$SiO_2-TiO_2-M_xO_y$ (M = Co, Cr or Cu)계의 비정질 박막을 현미경용 슬라이드 유리판 위에 전구체 용액을 스핀코팅방법으로 제조하였다. 전구체 용액은 tetraethyl orthosilicate, titanium trichloride, 그리고 코발트질산염, 크롬질산염, 구리질산염을 사용하여 합성하였다. X-선 회절분석 (${\theta}-2{\theta}$ scan)을 통하여 박막내에 $Co_3O_4$, $Cr_2O_3$, CuO 결정의 석출이 없는 비정질 박막임을 확인하였다. 코발트는 4면체배위의 $ Co^{2+}$로, 크롬은 4면체정배위의 $Cr^{6+}$로, 구리는 8면체배위의 $Cu^{2+}$로 존재하였다. 이 비정질박막의 표면에서 crack과 texture는 발견할 수 없었으며 파단면에서 박막악과 유리판 간의 계면은 균일한 조직을 보였다.

• 한국자기학회지
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• 제5권5호
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• pp.880-894
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• 1995

B의 함유량을 6 at% 고정하고 Nd함유량을 3~5 at%로 변화시킨 $\alpha$-Fe기 Nd-Fe-B 합금의 자기특성이 조사 되었다. 급속응고법으로 제조된 $Nd_{x}{(Fe_{0.9}Co_{0.1})}_{90-x}B_{6}Nb_{3}Cu_{1}(x=\;3,\;4,\;5)$ 비정질합금은 열처리에 의하여 초미세결정립으로 결정화하며, Nd의 함유량에 따라 잔류자화 및 보자력이 변한다. x=3의 경우 최적열처리조건에서 $\alpha$-Fe(Co) 부피분율의 증가로 잔류자 화는 증가하나, 보자력은 감소한다. 그러나 Nd 함유량의 증가는 $Nd_{2}{(Fe,\;Co)}_{14}B$ 부피분율의 증가로 인하여 잔류자화는 감소하나 보자력은 향상된다. $640^{\circ}C$, 10 min 열처리조건에서 $Nd_{5}{(Fe_{0.9}Co_{0.1})}_{85}B_{6}Nb_{3}Cu_{1}$의 결정립크기는 약 20 nm이며, 잔류자화, 보자력 및 최대에너지적 은 각각 1.35 T, 219 kA/m (2.75 kOe) 및 $129\;kJ/m^{3}$ (16.2 MGOe)으로 가장 우수하다.

• 한국자기학회지
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• 제17권3호
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• pp.128-132
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• 2007

큰 비정질 형성능을 가지는 FeSiBNb 비정질 리본 합금의 열적 및 자기적 특성에 미치는 Co의 첨가 효과에 대하여 연구되었다. 두께 $40\;{\mu}m$의 비정질$(Fe_{1-X}Co_X)_{72}Si_4B_{20}Nb_4(x=0{\sim}0.5)$ 합금에 대한 열분석 결과, Fe에 대한 Co의 치환량이 증가할수록 과냉각 액상의 존재 온도 범위가 넓어져 비정질 형성능이 증가하는 것으로 평가되었다. 또 Co 농도의 증가에 따라 약간의 $B_8$(800A/m에서의 유도 자속밀도)의 감소가 얻어지나, 투자율이 현저하게 증가하고 철손이 크게 감소하는 경향을 나타내었다. 한편 두께가 두꺼운 상기 비정질 합금의 교류 투자율의 주파수 특성은 와전류에 의한 표피 효과의 증대 때문에 $20\;{\mu}m$ 정도의 두께를 가지는 통상의 비정질 리본 합금에 비해 열화되는 것으로 나타났다.

• 전기화학회지
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• 제6권4호
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• pp.266-270
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• 2003

우수한 전기화학적 특성을 갖는 $LiN_{0.8}Co_{0.2}O_2$ 정극 활물질을 평균 $1{\mu}m$ 이하의 균일한 입자 분포를 얻을 수 있는 액상 반응법의 하나인 졸겔법을 이용하여 제조하였다. 제조된 $LiN_{0.8}Co_{0.2}O_2$를 X선 회절과 TEM(transmission electron microscopy)분석을 통하여 미세구조를 분석하였다. 충방전 실험전과 실험후의 미세구조의 변화에 중점을 주어 실험하였으며, 그 결과 졸겔법으로 제조된$LiN_{0.8}Co_{0.2}O_2$ 정극 활물질은 높은 가역 용량을 가지며 뛰어난 싸이클 특성을 가지고 있다 이는 졸겔법으로 제소함으로 인하여 Ni과 Co양이온의 균일한 화학조성을 가지고 있기 때문이라 생각된다. 특히 $LiCoO_2$에서 관찰되었던 cubic spinel disordering과 심각한 구조적 결함이 관찰되지 않았다. 또한 Al 치환으로 인하여 싸이클 특성을 좋아졌지만 용량은 감소하였다.