• Journal of Information Display
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• v.2 no.3
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• pp.13-17
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• 2001

The manganese-doped magnesium tin oxide with spinel structure was selected as a green phosphor for FED application and was synthesized by the solid state reaction. Its luminescence properties were investigated under low-voltage electron excitation. The $Mg_2SnO_4$:Mn phosphor showed green emission with the spectrum centered at 500 nm due to energy transfer from $^4T_1$ to $^6A_1$ of $Mn^{2+}$ ion. Optimum Mn concentration was 0.6 mole % and the decay time was shorter than 10 ms.

• Journal of the Korean Ceramic Society
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• v.24 no.2
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• pp.179-185
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• 1987

The microstructure and the electrical conductivity of MgO-doped Cr2O3 were investigated as a function of oxygen partial presure, temperature, and MgO content. The grain size was estimated about 1.0$\mu\textrm{m}$. The solubility limit is increased with oxygen partial pressure. Above the solubility limit of MgO in Cr2O3, the spinel phase(MgCr2O4) is formed by the reaction of MgO and Cr2O3. The electrical conductivity of MgO-doped Cr2O3 within the solubility limit is increased with MgO content. Above the solubility limit, however, it is decreased with increasing MgO content because of the formation of the spinel phase.

• 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.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.399-409
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• 1999

Mullitization of kaolinite and dickite was examined with special attention to the influence of polytypism and impurities on the phase transformation. The phase transformation sequence in dickite is identical with that in kaolinite except that cristobalite is crystallized at $50^{\circ}C$ higher temperature in dickite. Difference in phase transformation above $1000^{\circ}C$ in kaolin minerals is attributed to the different crystal structures of metadickite and metakaolinite on the effect of impurities. A part of quartz is transformaed into cristobalite. Spinel-type phase produced in disordered kaolins including illite occurs over a short range of temperatures. Primary mullite is transformed into orthorhombic mullite at higher temperature as well. These results sustain the idea that disintegration of methkaolin and the spinel-type phase supplies extra sillica and promotes the growth of mullite cristobalite.

• Journal of the Korean Applied Science and Technology
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• v.17 no.1
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• pp.49-53
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• 2000

For decompose carbon dioxide, manganese oxide was synthesized with $0.25M-MnSO_{4}{\cdot}nH_{2}O$ and 0.5M-NaOH by coprecipitation. We made magnetite deoxidized manganese oxide by hydrogen reduction for 1hour at $330^{\circ}C$. We investigated characteristics of catalyst, hydrogen reduction degree and decomposition rate of carbon dioxide. The structure of the hausmannite certified spinel type. The specific surface area of synthesized hausmannite and deoxidized hausmannite were $22.36m^{2}/g$, $33.56m^{2}/g$ respectively. The decomposition rate of $CO_{2}$ of deoxidized hausmannite was 57%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.281-285
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• 1998

The microstructure and conduction characteristics of ZnO varistor fabricated in the range of 0.0 ~ 4.0mol% $Y_20_3$ were investigated. With increasing$Y_20_3$ content, distribution of spinel phase decreased, whereas Y-rich phase segregated to the nodal point increased, as a result, the average grain size decreased in the range of $20.0 ~ 4.8{\mu}m$. $Y_20_3$ content showing relatively good conduction characteristics was l.Omol%, then nonlinear exponent and leakage current was 55.3, 0.66mA.respectively.

• Korean Journal of Crystallography
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• v.12 no.1
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• pp.20-24
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• 2001

NiZn-ferrite was synthesized usign waste iron oxide catalysts which were produced from styrene monomer process and buried underground as an industrial wastes. The spinel type ferrite was obtained by calcination and sintering of the mixture of finely ground waste catalysts, nickel oxide and zinc oxide powders. The sintered body of Ni/sub 0.5/Zn/sub 0.5/Fe₂O₄ composition at 1230℃ for 5 hours showed the density of 5.38g/㎤, and initial permeability of 59 at 1 kHz. Not only cerium oxide, which existed as a major component in the catalyst, but also unicorporated NiO and ZnO into spinel structure remained as second phases after sintering.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.110-114
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• 2003

LiAl/sub 0.24/Mn/sub 1.76/O/sub 4-y/S/sub y/ (y=0, 0.02) were synthesized by the sol-gel method. Both structures were refined by Rietveld method, its structure refined as a cubic spinel, space group Fd-3m, a=8.17937(30) Å and 8.18331(19) Å respectively. Though it has been made a charge/discharge experiment above 20 times, there was no change of 3 V/4 V capacity degradation. It was considered that the volume change of MnO/sub 6/ octahedron induced by sulfur substitution plays a key role in keeping the 3 V/4 V capacity. The refined composition of the compound could be confirmed with the ICP analysis.

• Korean Journal of Crystallography
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• v.15 no.1
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• pp.44-50
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• 2004

Spinel structured lithium managanese oxide $(LiMn_2O_4)$ powder with well defined facetted morphology was prepared by precipitation-evaporation method. {111}, {110}, and {100} planes are mainly observed in the $LiMn_2O_4$ powder. And powder shape of tetradecahedron and octahedron was observed depending on the calcinations temperature. The observed powder morphology observed seemed to be related to the nonstoichiometry of the oxygen in the $LiMn_2O_4$ spinel structure. Oxygen nonstoichiometry might be responsible for the Jahn-teller effect and structure transition which in turn affects the surface energy of the {111}, {110}, and {100} planes. Powder shape transition from tetradecahedron to octahedron seemed to be related to the surface energy of the {111}, {110}, and {100} planes with oxygen nonstoichiometry.

• Korean Journal of Materials Research
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• v.16 no.9
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• pp.578-583
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• 2006

We studied the physical properties of Ni-Zn ferrites by adding different chemicals such as $SO_4$, Cl, and $NO_3$. Specimens were prepared by the coprecipitation method and sintered at temperatures $950^{\circ}C,\;1,150^{\circ}C,\;and\;1,350^{\circ}C$, respectively. X-ray diffractions showed a spinel structure and the optical microscopy revealed grain size of 0.3 to 0.6 ${\mu}m$. The optimum sintering temperature to obtain fine, sintered microstructure depended on the additive : Cl and $NO_3\;at\;950^{\circ}C\;and\;SO_4\;at\;1,150^{\circ}C$. According to particle size analysis, higher magnetic permeability and magnetization value were observed with Cl and $NO_3\;than\;SO_4$. As sintering temperature was raised from $950^{\circ}C$ to $1,350^{\circ}C$, the average grain diameter, initial permeability and the magnetic moment also increased.