• Journal of Electrochemical Science and Technology
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• v.5 no.1
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• pp.32-36
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• 2014

The $0.3Li_2MnO_3{\cdot}0.7LiMn_{0.55}Ni_{0.30}Co_{0.15}O_2$ cathode material was prepared via a co-precipitation method. The vapor grown carbon fiber (VGCF) was used as a conductive material and its effects on electrochemical properties of the $0.3Li_2MnO_3{\cdot}0.7LiMn_{0.55}Ni_{0.30}Co_{0.15}O_2$ cathode material were investigated. From the XRD pattern, the typical complex layered structure was confirmed and a solid solution between $Li_2MnO_3$ and $LiMO_2$ (M = Ni, Co and Mn) was formed without any secondary phases. The VGCF was properly distributed between cathode materials and conductive sources by a FE-SEM. In voltage profiles, the electrode with VGCF showed higher discharge capacity than the pristine electrode. At a 5C rate, 146 mAh/g was obtained compared with 232 mAh/g at initial discharge in the electrode with VGCF. Furthermore, the impedance of the electrode with VGCF did not changed much around $9-10{\Omega}$ while the pristine electrode increased from 21.5${\Omega}$ to $46.3{\Omega}$ after the $30^{th}$ charge/discharge cycling.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.329-330
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• 2006

본연구에서는 초음파 모터 등의 고출력 액츄에이터에 응용 가능한 $0.4Pb(Ni_{1/3}Nb_{2/3})O_3$-$0.6Pb(Zr_{0.405}Ti_{0.595})O_3$ + 0.25wt% $Fe_2O_3$ 조성시스템에 $MnO_2$ (0~1 wt.%)첨가하여 압전, 유전특성 및 미세구조에 관해 고찰하였다. 본조성을 $1125{\sim}1175^{\circ}C$ 온도에서 2시간 소결하여 시편을 제조하였으며 이의 결정구조 및 미세조직을 분석하였다. $MnO_2$ 첨가량 증가에 따라 압전 상수와 전기기계결함계수는 감소하였으며, 기계적 품질계수는 0.5 wt% 첨가시까지 증가하였으나 첨가량이 그 이상 증가함에 따라 감소하였다. 압전특성은 $1125^{\circ}C$에서 소결한 $MnO_2$ 0.5wt%조성에서 ${\varepsilon}r$ = 2040, kp = 0.66, $d_{33}$ = 504, Qm=438의 우수한 특성을 나타내었다.

• Nuclear Engineering and Technology
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• v.46 no.1
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• pp.117-124
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• 2014

The effect of various process variables on the powder properties of recycled $U_3O_8$ from MnO-$Al_2O_3$ doped large grain $UO_2$ pellets and the effect of those recycled $U_3O_8$ powders on the sintered density and grain size of MnO-$Al_2O_3$ doped large grain $UO_2$ pellets have been investigated. The evolution of morphology, size, and BET surface area of the recycled $U_3O_8$ powders according to the respective variation of the thermo-mechanical treatment variables of oxidation temperature, powder milling, and sequential cyclic heat treatment of oxidation and then reduction was examined. The correlation between the BET surface area of recycled $U_3O_8$ powder and the sintered pellet properties of MnO-$Al_2O_3$ doped pellets showed that the pellet density and grain size of doped pellets were increased and then saturated by increasing the BET surface area of the recycled $U_3O_8$ powder. The density and grain size of the pellets were maximized when the BET surface area of the recycled $U_3O_8$ powder was in the vicinity of $3m^2/g$. Among the process variables applied in this study, the cyclic heat treatment followed by low temperature oxidation was a potential process combination to obtain the sinter-active $U_3O_8$ powder.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.23-27
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• 2006

By substituting Mn or Cr for Co in inverse spinel $CoFe_2O_4,\;Mn_xCo_{1-x}Fe_2O_4\;and\;Cr_xCo_{1-x}Fe_2O_4$ and thin films were prepared by sol-gel method and their structural and magnetic properties were investigated. X-ray diffraction indicates that the cubic lattice constant increase for the Mn substitution while it hardly changes for the Cr substitution. Substitution of $Mn^{2+}$ for octahedral $Co^{2+}$ sites can explain the increase of lattice constant in $Mn_xCo_{1-x}Fe_2O_4$. On the other hand, Substitution of $Cr^{3+}$ for octahedral $Co^{2+}$ and subsequent reduction of $Fe^{3+}$ ion into $Fe^{2+}$ are expected to happen. Mossbauer spectroscopy measurements on $Cr_xCo_{1-x}Fe_2P_4$ indicate the existence of tetrahedral $Fe^{2+}$ ions that are created through reduction of tetrahedral $Fe^{3+}$ ions in order to compensate charge imbalance happened by $Cr^{3+}$ substitution for octahedral $Co^{2+}$ sites. On the other hand, no $Fe^{2+}$ ions were detected by Mossbauer spectroscopy for $Mn_xCo_{1-x}Fe_2O_4$. A migration of $Fe^{3+}$ ions from octahedral to tetrahedral sites In $Mn_xCo_{1-x}Fe_2O_4$ was detected by Mossbauer spectroscopy for x>0.47. Vibrating sample magnetometry measurements on the samples at room temperature revealed that the saturation magnetization increases by Mn and Cr substitution for certain range of x, qualitatively explainable in terms of the comparison of spin magnetic moment among the related transition-metal ions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.936-941
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• 2010

In this study, we have investigated the effects of Mn dopant on the bulk trap levels and grain boundary characteristics of $Bi_2O_3$-based ZnO (ZB) varistor using admittance spectroscopy and dielectric functions (such as $Z^*,\;Y^*,\;M^*,\;\varepsilon^*$, and $tan\delta$). Admittance spectra and dielectric functions show two bulk traps of $Zn_i^{..}$ (0.20 eV) and $V^{\bullet}_o$ (0.29~0.33 eV) in ZnO-$Bi_2O_3-Mn_3O_4$ (ZBM). The barrier of grain boundaries in ZBM could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.79 eV at lower temperature to 1.08 eV at higher temperature. The grain boundary capacitance $C_{gb}$ was decreased slightly with temperature as 1.3~1.8 nF but resistance $R_{gb}$ decreased exponentially. The relaxation time distribution can result from the heterogeneity of the barriers constituting the varistor. It is revealed that Mn dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.

• Journal of Magnetics
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• v.17 no.3
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• pp.168-171
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• 2012

Irreversible magnetization between the zero-field-cooled (ZFC) and field-cooled (FC) states in $Y_{1-x}Sr_xMnO_3$ (x=0 and 0.2) was investigated. $YMnO_3$ and $Y_{0.8}Sr_{0.2}MnO_3$ have a hexagonal structure and the lattice parameter a decreases from 7.4408 ${\AA}$ to 7.4327 ${\AA}$ while c increases from 12.2244 ${\AA}$ to 12.2287 ${\AA}$ for $YMnO_3$ and $Y_{0.8}Sr_{0.2}MnO_3$, respectively. An anomaly is observed at around 74 K in ZFC and FC magnetization measurements for $YMnO_3$, whereas in $Y_{0.8}Sr_{0.2}MnO_3$ the ${\sigma}_{ZFC}$ and ${\sigma}_{FC}$ are split at low temperature, indicating glass-like behavior.

• Journal of Electrochemical Science and Technology
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• v.11 no.1
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• pp.50-59
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• 2020

Birnessite-type manganese dioxide (δ-MnO₂) with hierarchical micro-/mesoporosity was synthesized via sacrificial graphene template approach under mild hydrothermal conditions for the first time. Graphene template was obtained by a surfactant (cetyltrimethylammonium bromide, CTAB) assisted liquid phase exfoliation (LPE) in water. A thin PEDOT:PSS (poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate)) layer was applied to improve electrical conductivity and rate capability of MnO₂. The MnO₂ (535 F g^-1 at 1 A g^-1 and 45 F g^-1 at 10 A g^-1) and MnO₂/PEDOT:PSS nanocomposite (550 F g^-1 at 1 A g^-1 and 141 F g^-1 at 10 A g^-1) delivered electrochemical performances superior to their previously reported counterparts. An asymmetric supercapacitor, composed of MnO₂/PEDOT:PSS (positive) and Fe₃O₄/Carbon (negative) electrodes, provided a maximum specific energy of 18 Wh kg^-1 and a maximum specific power of 4.5 kW kg^-1 (ΔV= 2 V, 1M Na₂SO₄) with 85% capacitance retention after 1000 cycles. The graphene-templated MnO₂/PEDOT:PSS nanocomposite obtained by a simple and green approach promises for future energy storage applications with its remarkable capacitance, rate performance and cycling stability

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.865-868
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• 2000

It was examined that the relationship between microstructures, electrical properties and crystal structure of (1-x)CaMnO$_3$-xCaTiO$_3$solid solution system which was made by mixing a semiconducting material CaMnO$_3$of low resistance and a dielectric material CaTiO$_3$of high resistance with variable ratios (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0). As the CaTiO$_3$increased, the resistance, B constant and lattice constant were increased, but the grain size was decreased. On particular, above 50wt% of CaTiO$_3$, the resistance at 2 5$^{\circ}C$ was rapidly increased due to the correlation in connectivity of the lattices between the conductive Mn$^{+4}$ octahedron and the insulative Ti$^{+4}$ octahedron.ron.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1220-1221
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• 2006

[ $LiMn_2O_4$ ] powders for lithium ion batteries were synthesized from two separate raw material pairs of LiOH/MnO and $LiOH/MnO_2$. The powders prepared at 780 and $850^{\circ}C$ and their difference of electrochemical properties were investigated. Both powders calcined at 780 and $850^{\circ}C$ were composed of a single-phase spinel structure but those treated at $850^{\circ}C$ showed a lower intensity ratio of $I_{311}$ to $I_{400}$, a slightly larger lattice parameter, and an increased discharge capacity by 10% under $3.0{\sim}4.3V$ voltage range. The XPS study on the oxidation states of manganese repealed that powders made from LiOH/MnO had less $Mn^{3+}$ ion and gave better battery performances than those from $LiOH/MnO_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.346-347
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• 2006

기계적 품질계수(Qm)를 향상시키기 위해 $Y_2O_3$와 $MnO_2$를 첨가함에 따른 $SrBi_2Nb_2O_9$ 세라믹스의 강유전 특성을 알아보았다. 합성분말의 입도를 분석 한 결과 $SrBi_2Nb_2O_9$의 경우 781.27nm였고, $Y_2O_3$와 $MnO_2$를 첨가한 경우 각 각 830.4nm와 981.1nm로 particle size는 증가하였고, 소결 후 소결밀도는 차이가 거의 없었으며, grain size는 $SrBi_2Nb_2O_9$과 $Y_2O_3$를 첨가했을 경우 $1{\mu}m$이하이며 반면, $MnO_2$를 첨가하였을 때 결정립이 성장하여 $3{\sim}4{\mu}m$로 나타났다. 또한, 모두가 $450^{\circ}C$ 이상의 상전이온도를 갖았다.