• 한국전기화학회:학술대회논문집
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• 2004.04a
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• pp.20-20
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• 2004

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.121.1-121
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• 2003

• Journal of the Mineralogical Society of Korea
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• v.22 no.1
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• pp.63-72
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• 2009

Carbon-coated lithium iron phosphate ($LiFePO_4/C$) composites are synthesized by the modified mechanical activation method (modified MA process) and studied by the Rietveld structural refinement. Rietveld indices of $LiFePO_4/C$ indicate good fitting with $R_p=8.14%,\;R_{wp}=11.1%,\;R_{exp}=9.09%,\;R_B=3.88%$, and S (GofF, Goodness of fit) = 1.2, respectively. $LiFePO_4/C$ with a space group Pnma shows a = 10.3229(3)${\AA}$, b = 6.0052(2) ${\AA}$, c = 4.6939(1) ${\AA}$, and V = 290.98(1) ${\AA}^3$ in dimension, indicating good agreements with those of previous works. Synthetic powders are nano-sized ($65{\sim}90nm$) homogeneous particles with high purity. Thus the modified MA method will be an efficient process to get a high quality cathode material for commercial lithium batteries.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.121-125
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• 2006

[ $LiFePO_4$ ] is one of the promising materials for cathode material of secondary lithium batteries due to its high energy density, low cost, environmental friendliness and safety. $LiFePO_4$ was synthesized by the solid-state reaction method at 500 - 800°C. The crystal structure of $LiFePO_4$ was analyzed by X-ray powder diffraction. The samples synthesized at 600 and $700^{\circ}C$ showed a single phase of a olivine structure. The particle sizes were increased and the specific surface areas were decreased with heating temperatures. The electrochemical performance was investigated by coin cell test. The discharge capacities at 0.1 C-rate were 118 mAh/g and 112 mAh/g at $600^{\circ}C,\;700^{\circ}C$, respectively. In an attempt to improve the electrical conductivity of cathode materials, $LiFePO_4/graphite$ composite was prepared with various graphite contents. The electrical conductivity and discharge capacity were increased with increasing the graphite contents in composite samples. The rate capabilities at high current densities were also improved.

• Journal of the Korean Ceramic Society
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• v.32 no.3
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• pp.394-402
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• 1995

Electrical conductivity and thermoelectric power of the ferrous ferrite system of (Mg0.29-yMnyFe0.71)3-$\delta$O4 have been measured as function of the thermodynamic variables, cationic composition(y), temperature(T) and oxygen partial pressure(Po2) under thermodynamic equilibrium conditions at elevated temperatures. On the basis of the electrical properties-phase stability correlation, the stability regions of the ferrite spinel and its neighboring phases have been subsequently located in the log Po2 vs. y and log Po2 vs. 1/T planes in the ranges of 0 y 0.29, 1100 T/$^{\circ}C$ 1400 and 10-14 Po2/atm 1. The stability region, Δlog Po2(y, 1/T), of the ferrite spinel single phase widens with increasing Mn-content(y) and the boundaries of each region are linear against 1/T with negative slopes.

• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1491-1500
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• 1994

Nonstoichiometry($\delta$) and the phase stability region of a ferrite spinel (Mg0.29Fe0.71)3-$\delta$O4 have been investigated by a coulometric titration method as a function of temperature(T) and oxygen partial pressure(Po2). It has been found that the spinel is thermodynamically stable in the ranges -8.0$\leq$log(PO2/atm)$\leq$-2.4, -7.0$\leq$log(PO2/atm)$\leq$-1.7 respectvely at 100$0^{\circ}C$. The nonstoichiometry extends over the ranges of -0.004$\leq$$\delta$$\leq$0.007, -0.008$\leq$$\delta$$\leq$0.006, -0.033$\leq$$\delta$$\leq$0.004 at 100$0^{\circ}C$, 120$0^{\circ}C$, respectvely. The observed PO2-dependence of $\delta$ suggests that the majority ionic defects are cation interstitials in the low PO2 region and cation vacancies in the high PO2 region.

• Journal of Hydrogen and New Energy
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• v.22 no.5
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• pp.728-734
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• 2011

$LiFePO_4$ is a promising cathode material for secondary lithium batteries due to its high energy density, low cost and safety. $LiFePO_4$ was synthesized by the citrate process under reductive, neutral, and oxidative, atmospheres and the crystal structure was analyzed by X-ray powder diffraction. The samples synthesized under $N_2$ and $H_2$ atmosphere showed a single phase of a olivine structure, where the samples synthesized under $O_2$ atmosphere exhibited second phase of $Fe2O_3$. All the samples synthesized at 400, 600 and $800^{\circ}C$ under $N_2$ atmosphere presented a single phase of olivine. Residual organic material was observed for the sample synthesized at $400^{\circ}C$. There was nearly no intensity difference between the samples synthesized at $600^{\circ}C$ and $800^{\circ}C$. The electrochemical characteristic of the $LiFePO_4$ synthesized at $600^{\circ}C$ in the $N_2$ atmosphere was analyzed. The result exhibited an high discharge capacity of 160 mAh/g at the first cycle, and 155-160 mAh/g after 45 cycles.

• Bulletin of the Korean Chemical Society
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• v.7 no.5
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• pp.341-346
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• 1986

The electrical conductivity of the system ${\alpha}-Fe_2O_3-CoO$ was measured in the temperature range 200-1000$^{\circ}C$ and PO$_{2}$ range 10$^{-7}-2{\times}10^{-1}$ atm. Possible defect models were suggested on the basis of conductivity data, which were measured as a function of temperature and of oxygen partial pressure. The observed activation energies were 0.50 eV and 1.01 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on PO$_{2}$ were ${\sigma}\;{\alpha}\;PO_2^{-1/6}$ in the PO$_{2}$ range $10^{-7}-10^{-4}$ atm and ${\sigma}\;{\alpha}\;PO_2^{-1/4}$ at PO$_{2}$ 's of $10^{-4}-2{\times}10^{-1}$ atm at temperatures from 300-1000$^{\circ}C$. An extrinsic electron conduction due to an Vo defect and an intrinsic electron conduction due to an Fei' defect were suggested at different temperature and oxygen partial pressure regions, respectively.

• Journal of Korean Society of Forest Science
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• v.14 no.1
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• pp.21-31
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• 1972

It has intended to identify the members of the Genus Lespedeza in Korea by a chemical colour reaction, and the following five species of the Genus Lespedeza grown in the garden have been used in this experiment. 1. Lespedeza bicolor Turcz 2. Lespedeza bicolor var. melanantha (Nak.) T. Lee 3. Lespedeza cyrtobotrya Miq. 4. Lespedeza japonica var. intermedia Nakai 5. Lespedeza maritima Nakai 6. Lespedeza maximowiczii Schneider 7. Lespedeza maximowiczii var. tomentella Nakai A few drops of each solution of $K_2Cr_2O_7$. $FeSO_4{\cdot}7H_2O$, $FeCl_3$, $KH_2PO_4$, $KMnO_4$, $NH_4OH$, and HCl was added to the methanol extracts of wood dust to get the specific colour reaction. HCl-infused wood was also used for the identification of L. bicolor var. melanantha and L. bicolor. The results can be summarized as the following key; 1. Chrome lemon by $K_2Cr_2O_7$ ${\cdots}{\cdots}$2 1. Sun flower yellow by $K_2Cr_2O_7$ ${\cdots}{\cdots}$Lespedeza maximowiczii var. tomentella Nakai 2. $KH_2PO_4$ Oystem white by $KH_2PO_4$; golden yellow by $FeCl_3$ ${\cdots}{\cdots}$=3 2. Cream colour by $KH_2PO_4$=6 3. Oyster white by $NH_4OH$; corn colour by $FeSO_4{\cdot}7H_2O$ ${\cdots}{\cdots}$4 3. Cream colcur by $NH_4OH$ ${\cdots}{\cdots}$5 4. Van dyke brown by $KMnO_4$ ${\cdots}{\cdots}$; sea shell pink by HCl injection under heating ${\cdots}{\cdots}$Lespedeza japonica var. intermedia Nakai 4. Sepia colour by $KMnO_4$; honey colour by HCl injection under heating ${\cdots}{\cdots}$Lespedeza maritima Nakai 5. Golden red by $FeSO_4{\cdot}7H_2O$; andover green by HCl-infused wood dust ${\cdots}{\cdots}$Lespedeza bicolor var. melanantha (Nak.) T. Lee 5. Yellow ochre by $FeSO_4{\cdot}7H_2O$; sand warm gray by HCl-infused wood dust ${\cdots}{\cdots}$Lespedeza bicolor Turcz 6. Amber green by $FeCl_3$ ${\cdots}{\cdots}$Lespedeza cyrtobotrya Miq. 6. Leather brown by $FeCl_3$ ${\cdots}{\cdots}$Lespedeza maximowiczii Schneider.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.157-161
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• 2013

Porous $LiMn_{0.6}Fe_{0.4}PO_4$ (LMFP) was synthesized by a sol-gel process. Uniform dispersion of the conductive carbon source throughout LMFP with uniform carbon coating was achieved by heating a stoichiometric mixture of raw materials at $600^{\circ}C$ for 10 h. The crystal structure of LMFP was investigated by Rietveld refinement. The surface structure and pore properties were investigated by SEM, TEM and BET. The LMFP so obtained has a high specific surface area with a uniform, porous, and web-like nano-sized carbon layer at the surface. The initial discharge capacity and energy density were 152 mAh/g and 570 Wh/kg, respectively, at 0.1 C current density, and showed stable cycle performance. The combined effect of high porosity and uniform carbon coating leads to fast lithium ion diffusion and enhanced electrochemical performance.