• 한국세라믹학회지
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• 제44권12호
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• pp.660-682
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• 2007

An SOFC consists of all ceramic complex oxides each with different electrochemical-property requirements. These requirements, in principle, can be made met to a great extent by controlling or tailoring the defect structure of the oxide. This paper reviews the defect structure, nonstoichiometry as a measure of the total defect concentration, and the defect relaxation kinetics of complex oxides that are currently involved in a variety of growing applications today.

• 한국세라믹학회지
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• 제34권7호
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• pp.722-730
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• 1997

The nonstoichiometry (x) of UO2+x and (Er0.06U0.94)O2+x has been in-situ measure against oxygen activity (Po2) at elevated temperatures by a coulometric titration method. From the dependence of the oxygen excess (x) of UO2+x on Po2 at 1000℃, it has been concluded that (2Vo2Oia2Oib)〃〃and (2Vo2Oia2Oib)' clusters are prevailing at low oxygen partial pressure [log(Po2/atm) -10.6] and at high oxygen partial pressure [log(Po2/atm) -10.6], respectively. The nonstoichiometry is found to be reduced with the addition of Er, which is ascribed to the fact that the fixed-valent Er3+ reduces the oxidation capacities of UO2+x. The enthalpy of oxygen incorporation in (Er0.06li0.94)O2+x has been evaluated from the mean valences of U-ion as -180±70 kJ/mole.

• 연구논문집
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• 통권25호
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• pp.185-192
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• 1995

The solid/liquid interface migration in Nb-doped $SrTiO_3$ and its effect on dielectric properties have been investigated. The specimen sintered in air shows no migration during oxide infiltration treatment in air, whereas the specimen sintered in $5H_2-95N_2$ shows appreciable migration during similar infiltration. In the migrated layers of the specimen sintered in a reducing atmosphere, no cations of the infiltrants are detected by wavelength dispersive spectroscopy. These results show that nonstoichiometry due to the atmosphere change can induce the interface migration as in the case of frequently observed migrations due to solute concentration change. The driving force for the migration is discussed in terms of the coherency strain energy in a thin diffusional oxidized layer of the receding grain. The interface migration caused by nonstoichiometry could be suppressed by preoxidizing grain surfaces before oxide infiltration treatment. The suppression of migration increased the effective dielectric constant of the material.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 1998년도 춘계연구발표회 논문개요집
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• pp.66-67
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• 1998

• 공업화학
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• 제2권4호
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• pp.385-392
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• 1991

전하량적정법에 의해 $Ni_{1-x}O$의 비화학양(nonstoichiometry)를 측정하였고 결함모델을 확인하였다. 0.1-0.21atm의 산소분압과 1123-1198K의 온도범위에서 $Ni_{1-x}O$의 비화학양은 $Po_2{^{1/4}}$에 비례하였다. 이러한 산소분압의 의존성으로부터 $Ni_{1-x}O$의 주 결함은 singly 이온화한 Ni 빈자리임을 확인할 수 있었다. T=1173K와 $Po_2=0.21atm$인 조건에서 $x=1.21{\times}10^{-4}$의 값을 가졌다. 제안된 결함모델로 부터 결함의 표준생성엔탈피를 계산하였는데 0.95 eV의 값을 가졌다. 1248K 이상의 온도에서는 doubly 이온화된 빈자리로의 전이가 나타나기 시작하였다.

• 한국세라믹학회지
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• 제31권12호
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• pp.1491-1500
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• 1994

Nonstoichiometry($\delta$) and the phase stability region of a ferrite spinel (Mg0.29Fe0.71)3-$\delta$O4 have been investigated by a coulometric titration method as a function of temperature(T) and oxygen partial pressure(Po2). It has been found that the spinel is thermodynamically stable in the ranges -8.0$\leq$log(PO2/atm)$\leq$-2.4, -7.0$\leq$log(PO2/atm)$\leq$-1.7 respectvely at 100$0^{\circ}C$. The nonstoichiometry extends over the ranges of -0.004$\leq$$\delta$$\leq$0.007, -0.008$\leq$$\delta$$\leq$0.006, -0.033$\leq$$\delta$$\leq$0.004 at 100$0^{\circ}C$, 120$0^{\circ}C$, respectvely. The observed PO2-dependence of $\delta$ suggests that the majority ionic defects are cation interstitials in the low PO2 region and cation vacancies in the high PO2 region.

• 한국결정학회지
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• 제15권1호
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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.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.1927-1928
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• 2014

• The Korean Journal of Ceramics
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• 제6권2호
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• pp.177-182
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• 2000

At the porous $La_{0.6}Ca_{0.4}MnO_{3-{\delta}}$(LCM)/YSZ electrodes of solid oxide fuel cells (SOFC), the electrochemical redox reaction of oxygen proceeds via the triple boundary (TPB) of gas/LCM/YSZ. The surface diffusion of adsorbed oxygen on LCM has been proposed as the rate determining process, assuming the gradient of oxygen chemical potential from the outer surface of porous layer to TPB. Along with the formation of this gradient, oxygen nonstoichiometry in the bulk of LCM may varies. In this paper, an electrochemical technique was described precisely to determine the variation of oxygen content in LCM of porous LCM/YSZ under polarization. It was shown that the oxygen potential in LCM layer under large cathodic polarization is much lower than that in the gas phase, being determined from the electrode potential and Nernst equation.

• The Korean Journal of Ceramics
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• 제4권2호
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• pp.78-82
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• 1998

The oxygen nonstoichiometry (x) of UO$_{2+x}$ and $(Ce_yU_{1-y})O_{2+x}$ (y=0.05, 0.25) has been measured as a function of oxygen activity (a02) at 100$0^{\circ}C$ by a solid state coulometri titration technique. The results for UO$_{2+x}$ are in a good agreement with literature data and the ao2-dependence of the nonstoichimetry has been well explained with (2:2:2) cluster model. The equilibrium oxygen activity of $(Ce_yU_{1-y})O_{2+x}$ increases with Ce-content (y) for given nonstoichiometry (x), which is ascribed to the fact that Ce is present as Ce$^{3+}\; and\; Ce^{4+}$, and, therefore, the addition of Ce reduces the oxidation capacity of UO$_{2+x}$. From the oxygen activity dependence of x in $(Ce_yU_{1-y})O_{2+x}$ the defect structure of $(Ce_yU_{1-y})O_{2+x}$ is discussed.