• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.326-326
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• 2008

일반적인 고상반응법을 이용하여 $Eu^{2+}$ 활성화 $\alpha$-sialon 황색 형광체를 합성한 후 구조 및 광학특성을 측정하였다. $Ca^{2+}$와 $Si^{4+}$ 이온의 비화학양론적 첨가에 따른 광학 특성 측정결과, 중심 발광 파장이 약 585 nm 인 높은 휘도의 황색형광체를 얻을 수 있었다. 본 연구에서는 $Ca^{2+}:Si^{4+}$ 첨가비에 따른 광학특성 변화를 관찰하였으며, 이를 바탕으로 구조 및 미세구조 변화에 대한 연구를 수행하였다. 20 mol%의 Al deficient 조성을 갖는 형광체의 광학특성 측정결과 화학양론조성에 비해 20% 이상의 휘도향상을 나타내었다. 이와 같은 결과로부터, 본 연구에서 제시된 Al deficient $\alpha$-sialon 황색 형광체는 자외선 및 청색 LED용 형광체로 적합할 것으로 판단된다.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.33-39
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• 1986

The x-values of nonstoichiometry chemical formulas, Sm$O_{1.5+x}$ and Zr$O_{2+x}$, have been measured in temperature range from 500$^{\circ}$C to 1000$^{\circ}$C under oxygen pressure of 2 ${\times}10^{-1}$ to 1 ${\times}10^{-5}$ atm by gravimetric method. The enthalpies of formation of defect in samarium sesquioxide and zirconium dioxide decrease with decreasing oxygen pressure and are all positive. The 1/n values calculated from the slopes of the plots of log x vs. log $PO_2$ increase with temperature and are positive values which mean the higher oxygen pressure dependence at higher temperature. From x-values and thermodynamic data, it is found out that the nonstoichiometric defect is fully ionized metal vacancy. The conduction mechanisms of the systems are also discussed with respect to the nonstoichiometric compositions.

• Journal of the Korean Chemical Society
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• v.28 no.4
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• pp.231-237
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• 1984

The x-values in the nonstoichiometric chemical formulas $YO_{1.5+x}\;and\;HoO_{1.5+x}$, have been measured in the temperature range from 700$^{\circ}$C to 1000$^{\circ}$C under oxygen pressures from $2{\times}l0^{-1}\;to\;1{\times}10^{-6}$ atm by gravimetric method. The observed x-values increase with increasing temperature and oxygen pressure. The enthalpies of formation of excess oxygen in yttrium oxide and holmium oxide decrease with decreasing oxygen pressure and are all positive values representing an endothermic process. The 1/n values calculated from the slopes of the plots of log x vs. log $P_{O2}$ increase with temperature and are positive values which means the higher oxygen pressure dependence at higher temperature. We have examined the nonstoichiometric defect and conduction mechanism from x-values and thermodynamic data.

• Journal of the Korean Chemical Society
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• v.33 no.1
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• pp.25-30
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• 1989

The nonstoichiometry and electrical conductivities of Tm$_2O_3$ were studied in the oxygen pressure $2\;{\times}\;10^{-1}\;-1\;{\tiems}\;10^{-4}$ atm under the temperature ranges from 700 to 1100$^{\circ}$C. The x values of $TmO_{1.5+X}$ were varied in the ranges of 0.1004∼0.0110. The enthalpies of formation of the nonstoichiometric compounds were found to be 5.40-4.71 kcal/mole, and the average activation energy obtained from the plots of log conductivity vs. 1000/T was 1.65 eV. The Po$_2$ dependencies of the electrical conductivity were found to be linear and closely approaximated to ${\sigma}{\alpha} PO{\frac{1}{2}^{/5.3}$ in the temperature range 700∼1100$^{\circ}$C. The nonstoichiometry and the electrical conductivity are due to trivalent metal vacancies.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.10a
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• pp.221.1-221
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• 2001

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.239.2-239
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• 2002

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.300.2-300
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• 2001

• Journal of the Korean Chemical Society
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• v.17 no.5
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• pp.337-345
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• 1973

The nonstoichiometry of the iron oxide system has been studied by analyzing the weight loss of a sample, measured by using a quartz microbalance, in a temperature range from $0^{\circ}C$ to $1200^{\circ}C$ under oxygen pressures from $10^{2}mmHg$ to $10^{-4}mmHg$. The Y values of the formula, $FeO_{1+\gamma}$, that have been obtained by this means for various conditions of temperature and pressure in this range are considered to be more accurate than values obtained by methods requiring thste quenching of the sample before measurements are made. The plots of log Y vs $log PO_2$ (or $log Y =_n log PO_2$) show linearity and n calculated from the slope of the plot is about 1/10 at $1000^{\circ}C$, indicating a difference between the nonstoichiometric and oxidation mechanisms. The condition for the formation of stoichiometric FeO was determined to be $1200^{\circ}C$ under $10^{-3}mmHg$ of $O_2$ and the composition of the oxide under standard conditions was $FeO_{1.11185}$. As in general more oxygen dissolves into the oxide system at lower temperatures and higher oxygen pressures, the deviation from stoichiometric FeO is greater under those conditions. A comparison of the change in conductivity of the sample indicates that full phase transition does not take place with conductivity transition.

• Journal of the Korean Chemical Society
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• v.36 no.4
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• pp.511-516
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• 1992

The x-values of the nonstoichiometric compound YbO$_x$ have been measured in a temperature range of 600 to 1150$^{\circ}C$ under oxygen partial pressure of 1.00 ${\times}$ 10$^{-2}$ atm∼atmospheric air pressure. The values are varied between 1.55453 and 1.60794 in the conditions. The enthalpy of the formation for x' in YbO$_{1.5＋x'}$(${\Delta}$H$_f$) was 1.55, 1.18, and 1.05 kJ/mol under the above conditions, respectively. The electrical conductivities of the oxides or ${\sigma}$ have been measured in the temperature range from 600 to 1100$^{\circ}C$ under oxygen partial pressure of 1.00 ${\times}$ 10$^{-5}$ ∼ 2.00 ${\times}$ 10$^{-1}$ atm. They varied from 10$^{-9}$ to 10$^{-5}$ ohm$^{-1}$ cm$^{-1}$ within the semiconductor range. The Arrhenius plots of the electrical conductivities show a linearity and the activation energy for the conduction was about 1.7eV. The oxygen partial pressure dependence of the conductivity or 1/n value increases with the pressure. The nonstoichiometric conduction mechanism of the oxide was discussed in terms of the x values, ${\sigma}$ values, and the thermodynamic data.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.21-26
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• 1995

The systematic variation of complex permeability and complex permittivity and their relationship with micro-wave absorbing properties are investigated in sintered Ni-Zn ferrites of non-stoichiometric composition. The specirrens of ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ spinels were prepared by a conventional ceramic processing technique. In the present study. complex permeability and permittivity can be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the spinel lattice. The primary effect of the excess ${\alpha}-Fe_{2}O_{3}$ is to increase the dielectric constant. while the notable decrease of magnetic loss is observed in the iron-deficient ferrites. The results suggest that the matching fre-queocyand matching thickness could be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the Ni-Zn ferrite.