• Korean Journal of Materials Research
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• v.22 no.12
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• pp.675-681
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• 2012

We aimed to examine the co-doping effects of 1/6 mol% $Mn_3O_4$ and 1/4 mol% $Cr_2O_3$ (Mn:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Cr-doped ZBS, ZBS(MnCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ (also ${\beta}-Bi_2O_3$ at Sb/Bi ${\leq}$ 1.0) were detected for all of the systems. Mn and Cr are involved in the development of each phase. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 system by Mn rather than Cr doping. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(MnCr), the varistor characteristics were improved dramatically (non-linear coefficient, ${\alpha}$ = 40~78), and seemed to form ${V_o}^{\cdot}$(0.33 eV) as a dominant defect. From impedance and modulus spectroscopy, the grain boundaries can be seen to have divided into two types, i.e. one is tentatively assigned to ZnO/$Bi_2O_3$ (Mn,Cr)/ZnO (0.64~1.1 eV) and the other is assigned to the ZnO/ZnO (1.0~1.3 eV) homojunction.

• Journal of the Korean institute of surface engineering
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• v.35 no.4
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• pp.193-198
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• 2002

Alloys of XD45 (Ti45A12Nb2Mn-0.8vol%TiB$_2$) and XD47 (Ti47A12Nb2Mn-0.8vol%TiB$_2$) were oxidized between 800 and $1000^{\circ}C$ in air, and their oxidation characteristics were studied. The oxide scales consisted primarily of an outer $TiO_2$ layer, an intermediate $Al_2$$O_3$-rich layer, and an inner mixed layer of ($TiO_2$+$Al_2$$O_3$). Nb tended to present at the lower part of the oxide scale, whereas Mn at the upper part of the oxide scale. The Pt marker tests indicated that the outer oxide layer grew primarily by the outward diffusion of Ti and Mn, and the inner mixed layer by the inward transport of oxygen.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.332-337
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• Journal of Magnetics
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• v.11 no.1
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• pp.12-15
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• 2006

Magnetic and electronic properties of reduced rutile titanium dioxide $(TiO_{2-\delta})$ thin films doped by Mn have been investigated. The present sol-gel-grown semiconducting $TiO_{2-\delta}:Mn$ films exhibit a ferromagnetic behavior at room temperature for a limited range of Mn content. The Mn-doped films have p-type electrical conductivity with the carrier concentration near $10^{19}\;cm^{-3}$. The observed room-temperature ferromagnetism is believed to be intrinsic but not related to free carriers such as holes. Oxygen vacancies are likely to contribute to the room-temperature ferromagnetism-trapped carriers in oxygen vacancies can mediate a ferromagnetic coupling between neighboring $Mn^{+3}$ ions. The energy band-gap change due to the Mn doping measured by spectroscopic ellipsometry exhibits a red-shift compared to that of the undoped sample at low Mn content. It is explainable in terms of strong spin-exchange interactions between Mn ion and the carrier.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.4
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• pp.205-210
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• 2003

Various types of high strength steel sheets were usually used for improving the automobile safety and fuel efficiency by reducing the vehicle weight. The present study aimed to develop the TRIP (transformation induced plasticity) aided high-strength low carbon steel sheets by using a reverse transformation process. The 0.1C-4~8Mn steels were reverse-transformed by slow heating to intercritical temperature region and then furnace cooled to the room temperature. Granular type retained austenite was observed in 4Mn steel and lath type retained austenite was also observed in 6~8Mn steel. The results show that the 6Mn steel under reverse transformed at $625^{\circ}C$ for 6 hrs has maximum elongation up to 39%. The optimum strength-elongation combination was 3,888 ($kg/mm^2{\times}%$) when the 8Mn steel was reverse transformed at $625^{\circ}C$ for 12 h.

• Korean Journal of Metals and Materials
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• v.50 no.6
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• pp.419-425
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• 2012

The purpose of this research was to develop a low Ni austenitic cast iron through replacing Ni by Cu and Mn because they are cheaper than Ni. The effect of the Cu content (6-12 wt%) on the microstructure characteristics was investigated in Fe-3%C-16%(Ni+Cu+Mn) cast iron. Contrary to general effect of the Cu on cast iron, the result of the microstructure analysis indicated that bainite and cementite were formed in high Cu content (>8 wt%Cu). A crystallized Cu-solution (Cu-Mn) phase and MnS in the Cu-solution were formed. The quantity of those phases increased as the Cu content increased. Consequently, the high Cu content in the composition ratio (Ni+Cu+Mn=16%) caused the formation of Cu-Mn/MnS and those phases decreased the effect of Cu and Mn on austenite formation. For this reason, bainite and cementite were formed in high Cu content.

• Journal of the Semiconductor & Display Technology
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• v.20 no.1
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• pp.12-17
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• 2021

The electronic and magnetic properties for Mn-adsorbed on the chalcopyrite (CH) AlGaP2 semiconductor are investigated by using first-principles FPLMTO method. The clean CH-AlGaP2 without adsorbed Mn is a p-type semiconductor with a direct band-gap. The Mn-adsorbed CH-AlGaP2 exhibits the ferromagnetic state. It is more energetically stable than the other magnetic ones. The interstitial site on P-terminated surface is more energetically favorable one than the Al/Ga-terminated surface, or the other adsorbing sites. In the case of Mn-adsorbed Al/Ga-terminated surface, it is induced a strong coupling between Mn-3d and neighboring P-3p electrons. The holes of partially unoccupied minority Mn-3d state and majority (or minority) Al-3p or P-3p state are induced. Thus a high magnetic moment of Mn is sustained by holes-mediated double-exchange coupling. It is noticeable that the semiconducting and half-metallic characteristics of CH-AlGaP2:Mn thin film is disappeared.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.10a
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• pp.12-13
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• 1997

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.2
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• pp.57-62
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• 2007

Willemite green phosphor powders have been prepared by the metallo-organic decomposition (MOD) method, and the photoluminescence and phase formation were studied as a function of both the firing temperature ($800{\sim}1100^{\circ}C$) and the concentration of Mn activator ($4{\sim}12 mol%$). Under 254 nm excitation source, the emission intensity of the phosphors increased with increasing the firing temperature from 800 to $1000^{\circ}C$. From the XRD analysis, the powders heat-treated above $1000^{\circ}C$ showed willemite crystal structure. The maximum emission intensity was obtained far the phosphors heat-treated at $1000^{\circ}C$ with 8 mol% of Mn content. The concentration quenching was occurred when the Mn concentration exceeded 10 mol%. The phosphor particles showed spherical shapes with the average size of $0.4{\sim}0.5{\mu}m$ by the SEM morphology.

• Korean Journal of Materials Research
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• v.12 no.9
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• pp.712-717
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• 2002

New wet chemical method so called precipitation-evaporation method was suggested for preparing spinel structure lithium manganese oxide ($LiMn_2$$O_4$) for Li ion secondary battery. Using precipitation-evaporation method, $LiMn_2$$O_4$ cathode materials suitable for Li ion secondary batteries can be synthesized. Single spinel phase $LiMn_2$$O_4$ powder was synthesized at lower temperature compared to that of prepared by solid-state method. $LiMn_2$$O_4$ powder prepared by precipitation-evaporation method showed uniform, small size and well defined crystallinity particles. Li ion secondary battery using $LiMn_2$$O_4$ as cathode materials prepared by precipitation-evaporation method and calcined at $800^{\circ}C$ showed discharge capacity of 106.03mAh/g and discharge capacity of 95.60mAh/g at 10th cycle. Although Li ion secondary battery showed somewhat smaller initial capacity but good cyclic ability. It is suggested that electro-chemical properties can be improved by controlling particle characteristics by particle morphology modification during calcination and optimizing Li ion secondary battery assembly conditions.