• Korean Chemical Engineering Research
• /
• v.57 no.4
• /
• pp.547-552
• /
• 2019

Electrochemical properties of $LiMn_{0.8}Fe_{0.2}PO_4$ cathode were investigated with gel polymer electrolyte (GPE). To access fast and efficient transport of ions and electrons during the charge/discharge process, a pure and well-crystallized $LiMn_{0.8}Fe_{0.2}PO_4$ cathode material was directly synthesized via spray-pyrolysis method. For high operation voltage, polyacrylonitrile (PAN)-based gel polymer electrolyte was then prepared by electrospinning process. The gel polymer electrolyte showed high ionic conductivity of $2.9{\times}10^{-3}S\;cm^{-1}$ at $25^{\circ}C$ and good electrochemical stability. $Li/GEP/LiMn_{0.8}Fe_{0.2}PO_4$ cell delivered a discharge capacity of $159mAh\;g^{-1}$ at 0.1 C rate that was close to the theoretical value ($170mAh\;g^{-1}$). The cell allows stable cycle performance (99.3% capacity retention) with discharge capacity of $133.5mAh\;g^{-1}$ for over 300 cycles at 1 C rate and exhibits high rate-capability. PAN-based gel polymer is a suitable electrolyte for application in $LiMn_{0.8}Fe_{0.2}PO_4/Li$ batteries with perspective in high energy density and safety.

• Journal of the Korean Magnetics Society
• /
• v.4 no.3
• /
• pp.226-232
• /
• 1994

Rapidly solidified $SmFe_{7+x}M_{x}(M=Mo,\;V,\;Ti)$ compound were found to crystallize in the ${Sm(Fe,\;M)}_{7}$ based stable magnetic phase by introducing a second transition element into the Sm-Fe binary system. The ${Sm(Fe,\;M)}_{7}$ phase exhibits the highest Curie temperatuer ($T_{c}=355^{\circ}C$) ever Known in the Sm-Fe magnetic systems with a quite high intrinsic coercivity($_{i}H_{c}=3~6\;kOe $). The ${Sm(Fe,\;M)}_{7}$ phase remains stable even after annealing if once form during the rapid solidification. The primary reason for the high coercive force is due to the fine grain size($2000~8000\;{\AA}$)of the magnetic ${Sm(Fe,\;M)}_{7}$ matrix phase, and the enhanced Curie temperature is attributed to the extended solid-solubility of the additive transition elements in Fe matrix, which leads to volume expansion of the ${Sm(Fe,\;M)}_{7}$ cell causing an enhanced coupling constant of Fe atoms.

• Journal of the Korean Magnetics Society
• /
• v.5 no.3
• /
• pp.191-196
• /
• 1995

NiCuZn ferrites were prepared by a solid-state reaction and sintered at $900^{\circ}C$ for 5 hours. Its properties were investigated by controlling the ferrite composition and processing. NiCuZn ferrite with a composition of ${(Ni_{0.2}Cu_{0.2}Zn_{0.6}O)}_{1.02}{(Fe_{2}O_{3})}_{0.98}$ was found to have the maximum initial permeability as a result of the variation of Cu content and the (Ni+Cu)/Zn ratio. Curie temperature($T_{c}$) of NiCuZn ferrite was decreased with the larger Cu content and increased with the larger Ni content. NiCuZn ferrites of ${(Ni_{0.2}Cu_{0.2}Zn_{0.6}O)}_{1-w}{(Fe_{2}O_{3})}_{1+w}$ composition milled for 20~80 hours had the maximum initial permeability at w=-0.015 and Curie temperature ($T_{c}$) was decreased with the increasing of $Fe_{2}O_{3}$ deficiency(w).

• Journal of Sensor Science and Technology
• /
• v.30 no.2
• /
• pp.94-98
• /
• 2021

In this study, pure and Co3O4/CoFe2O4-loaded Indium oxide (In2O3) nanofibers were synthesized by the electrospinning of an Indium/Polyvinylpyrrolidone precursor solution containing cobalt and iron bimetallic zeolitic imidazolate frameworks and subsequent heat treatment. The ethanol, toluene, p-xylene, benzene, carbon monodxide, and hydrogen gas sensing characteristics of the solution were measured at 250-400 ℃. 0.5 at%-Co3O4/CoFe2O4-loaded In2O3 nanofibers exhibited extreme response (resistance ratio - 1) to 5 ppm of ethanol (210.5) at 250 ℃ and excellent selectivity over the interfering gases. In contrast, pure In2O3 nanofibers exhibited relatively low responses to all the analyte gases and low selectivity above 250-400 ℃. The superior response and selectivity toward ethanol is explained by the catalytic roles of Co3O4 and CoFe2O4 in gas sensing reaction and the electronic sensitization induced by the formation of p (Co3O4/CoFe2O4)-n (In2O3) junctions.

• Journal of the Korean Chemical Society
• /
• v.38 no.2
• /
• pp.92-100
• /
• 1994

Ultrafine cobalt-substituted iron oxide particles were prepared by the thermal decomposition and oxidation of the new organometallic precursor, $Co_xFe_{1-x}(N_2H_3COO)_2(N_2H_4)_2$ (x = 0, 0.01, 0.02, 0.03, 0.05, 0.10, 1.00). The organometallic precursors were synthesized by the reaction of Co(II) and Fe(II) ion in a mole ratio of x : 1-x with hydrazinocarboxylic acid, and characterized by quantitative analysis, elemental analysis and infrared spectroscopy. The mechanistic study on the thermal decomposition of the organometallic precursors was performed by TG-DTG and DSC. The cobalt-substituted iron oxide particles were obtained by the heat treatment of the precursors at $350^{\circ}C$ and $450^{\circ}C$ for six hours in air. The prepared iron oxide was found to have two phases such as ${\gamma}-Fe_2O_3$ and a mixture of ${\gamma}-Fe_2O_3\;and\;{\alpha}-Fe_2O_3$ at $350^{\circ}C$ and $450^{\circ}C$ respectively. The particle shape was equiaxial and the particle size was less than 0.05 ${\mu}m.$ The coercivity and squareness of the cobalt substituted iron oxide particles increased with increasing cobalt content. Both coercivity and squareness showed higher values at $450^{\circ}C.$

• Journal of the Korean Magnetics Society
• /
• v.20 no.6
• /
• pp.222-227
• /
• 2010

$BiFeO_3$ (BFO) thin films were deposited on Pt/Ti/$SiO_2$/Si(100) substrates by RF magnetron sputtering method at room temperature. The influence of the flow rate of $O_2$ gas on the preparation of $BiFeO_3$ thin films was studied. XRD results indicate that the $BiFeO_3$ thin films were crystallized to the perovskite structure with the presence of small amount of impurity phases. The flow rate of $O_2$ gas has great affect on the microstructures and magnetic properties of $BiFeO_3$ thin films. As flow rate of $O_2$ gas increased, roughness and grain size of the thin films increased. $BiFeO_3$ thin films exhibited weak ferromagnetic behavior at room temperature. The PFM images revealed correlation between the surface morphology and the piezoresponse, indicating that the piezoelectric coefficient is related to microstructure.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1997.10a
• /
• pp.75-80
• /
• 1997

Ethanol을 용매로 사용한 iron(III) Nitrate(Fe(NO$_3$)$_3$.9$H_2O$) 용액의 가수분해 반응에 의해 $\alpha$-Fe$_2$O$_3$미분말을 합성하였다. 가수분해 정도를 알아보기 위해 pH 변화를 측정하였으며, 반응온도와 iron(III) nitrate의 농도를 변화시켜 각각이 입자크기에 미치는 영향을 관찰하였다. 하소 후의 XRD pattern을 관찰하여 $\alpha$-Fe$_2$O$_3$결정상의 생성을 확인하였으며, 미세구조 관찰 결과 얻어진 $\alpha$-Fe$_2$O$_3$분말은 50nm이하의 미세한 입자임이 확인되었다.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.8
• /
• pp.1545-1553
• /
• 2008

Using a one-pot reaction technique, monodisperse $\gamma-Fe_2O_3$ nanoparticles were prepared by thermal decomposition of Fe$(CO)_5$ in the presence of a long alkyl chain terminated dendron surfactant. The size of the particles is controlled by adjusting the concentration of the dendron ligands in the reaction solution. Spherical, 2 nm sized nanoparticles were obtained with a 3:1 ratio of dendrons to Fe$(CO)_5$, while 4.6 nm sized particles were formed with a 1:3 ratio. Superparamagetic properties of 2 nm, 4 nm, and 4.6 nm sized particles were measured using a SQUID magnetometer.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.29A no.11
• /
• pp.78-83
• /
• 1992

The current-voltage characteristics at SrO${\cdot}6Fe_{2}O_{3}$ electronic ceramics interfaces have been studied using cyclic voltammetric methods. The symmetrical and stable cyclic voltammograms, which indicate the same anodic and cathodic process, are obtained on the whole experiments. The approximate saturation current is 50$\mu$A but the value depends on the experimental processes of the electrode specimens. The current-voltage characteristics of SrO${\cdot}6Fe_{2}O_{3}$ electronic ceramics in dilute aqueous electrolytes or double deionized water are determined by the water adsorption process and the interconnected porosity effect. On the other hand, the current-voltage characteristics in relatively concentrate aqueous electrolytes are determined by the ionic adsorption process and the related electrical double layers. The SrO${\cdot}6Fe_{2}O_{3}$ electronic ceramics can be directly used as an electrochemically stabled resistor, electrode or a humidity sensor.

• Journal of Magnetics
• /
• v.19 no.1
• /
• pp.5-9
• /
• 2014

The amine functionalized $CoFe_2O_4$ nanoparticles were prepared by thermal decomposition method at reflux temperatures $160^{\circ}C$ and $172^{\circ}C$. The obtained $CoFe_2O_4$ nanoparticles at $160^{\circ}C$ reflux temperature show aggregation free poly-dispersed nanoparticles in 4-15 nm range. In an elevated reflux temperature of $172^{\circ}C$, $CoFe_2O_4$ show aggregated poly-dispersed nanoparticles in the size range of 20-46 nm. The saturation magnetization value at 300 K exhibited 51 emu/g at reflux temperature of $160^{\circ}C$. However, the sample synthesized at an elevated temperature of $172^{\circ}C$ has shown a coercive field value of 560 Oe with saturation magnetization of 68 emu/g.