• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.799-804
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• 2000

Coulometric titration experiments have been done for copper doped cobaltous oxide (Co1-xCux)1-$\delta$ O with various dopant concentrations. We present the obtained experimental data and compare our results to those of previous thermogravimetric investigation. The experimental data are fitted by theoretical calculations based on various defect models. For this modeling, we considered different types fo major defects like copper in substitutional and interstitial lattice sites as well as copper vacancy. We also introduced the copper evaporation effect during titration experiment into our consideration.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.56.1-56.1
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• 2009

The intermediate operating temperature of solid oxide fuel cells (IT-SOFCs) have achieved considerable importance in the area of power fabrication. This is because to improve materials compatibility, their long-term stability and cost saving potential. However, to conserve rational cell performance at reduced-temperature regime, cathode performance should be obtained without negotiating the internal resistance and the electrode kinetics of the cell. Recently, double perovskite structure cathodes have been studied with great attention as a potential material for IT-SOFCs. In this study, double-perovskite structured cathodes of $GdBaCoCuO_{5+\delta}$, $GdBaCo_{2/3}Cu_{2/3}Fe_{2/3}O_{5+\delta}$ compositions and $(1-x)GdBaCo_2O_{5+\delta}+xCe_{0.9}Gd_{0.1}O_{1.95}$ (x = 10, 20, 30 and 40 wt.%) composites were evaluated as the cathode for intermediate temperature solid oxide fuel cells(IT-SOFCs). Electrical conductivity of the cathodes were measured by DC 4-probe method, and the thermal expansion coefficient of each sample was measured up to $900^{\circ}C$ by a dilatometer study. Area specific resistances(ASR) of the $GdBaCo_{2/3}Cu_{2/3}Fe_{2/3}O_{5+\delta}$ cathode and 70 wt.% $GdBaCo_2O5+\delta$ + 30wt.% Ce0.9Gd0.1O1.95 composite cathode on CGO electrolyte substrate were analyzed using AC 3-probe impedance study. The obtained results demonstrate that double perovskite-based compositions are promising cathode materials for IT-SOFCs.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.33.1-33.1
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• 2011

Strontium doped lanthanum manganite (LSM) with perovskite structure for SOFC cathode material shows high electrical conductivity and good chemical stability, whereas the electrical conductivity at intermediate temperature below $800^{\circ}C$ is not sufficient due to low oxygen ion conductivity. The approach to improve electrical conductivity is to make more oxygen vacancies by substituting alkaline earths (such as Ca, Sr and Ba) for La and/or a transition metal (such as Fe, Co and Cu) for Mn. Among various cathode materials, $LaSrMnCuO_3$ has recently been suggested as the potential cathode materials for solid oxide fuel cells (SOFCs). As for the Cu doping at the B-site, it has been reported that the valence change of Mn ions is occurred by substituting Cu ions and it leads to formation of oxygen vacancies. The electrical conductivity is also affected by doping element at the A-site and the co-doping effect between A-site and B-site should be described. In this study, the $La_{1-x}Sr_xMn_{0.8}Cu_{0.2}O_{3{\pm}{\delta}}$ ($0{\leq}x{\leq}0.4$) systems were synthesized by a combined EDTA-citrate complexing process. The crystal structure, morphology, thermal expansion and electrical conductivity with different Sr contents were studied and their co-doping effects were also investigated.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.772-777
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• 1999

$Y_2Ba_1Cu_1O_5(Y211)$ powders were prepared by pyrophoric synthesis method and by solid state reaction method using $Y_2O_3(99.9%)$, $BaCO_3(99.9%)$, and CuO(99.9%) powders in both of these processes. The phase formation and reaction kinetics of $Y_2Ba_1Cu_1O_5$ powders have been studied using X-ray diffraction analysis(XRD) of samples at various heat treatment temperatures and reaction time. The reaction characterization suggested that the phase formation rate is mainly controlled by the particle size of Y211 powders. The activation energy(${\Delta}E_a$) of Y211 phase formation in this pyrophoric synthesis method was found to be 136.42 kJ/mol compared with 149.46 kJ/mol for that of solid state reaction method. These results data showed that the pyrophoric synthesis method is kineticaly more efficient than the solid state reaction method in this $Y_2Ba_1Cu_1O_5$ system.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.165-171
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• 1998

The $Y_1Ba_2Cu_3O_{7-x}$(123) superconductor powders were prepared by pyrophoric synthesis method(PSM) using $Y_2O_3$(99.9%), $BaCO_3$(99.9%), and CuO(99.9%) powders. The phase formation and reaction kinetics of 123 superconductor manufactured with powders prepared in various pHs of pyrophoric synthetic solution have been studied through the experiments at various heat treatment temperatures and times. Inductively coupled plasma(ICP) spectroscopy and scanning electron microscopy(SEM) measurements were performed to examine the composition and morphology of the sample. X-ray diffraction(XRD) analysis was done to determine phase formation and conversion ratio of Y-Ba-Cu-O systems. The 123 powder prepared at pH 7(${\pm}0.3$) yields the best result in terms of purity, homogeneity, and reactivity. The activation energies(${\Delta}E_a$) of 123 phase formation were found to be 191 kJ/mol and 230kJ/mol in solid state reaction method and pyrophoric synthesis method, respectively.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.164-167
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• 2000

The barium rich region of the Y-Ba-Cu-O-C system includes a tetragonal perovskite-like phase, which possesses a wide homogeneity region toward yttrium, copper and carbonate ion on the one hand, and toward oxygen, on the other hand. Accounting for vacancies ($\square$-vacancy) this phase could be described by the general formula per unit cell: {Ba$_8$}[Y$_{3-z}$Cu$_{5-x}$$(CO_3)_n$ $\square$$_{x+x-n}$]O$_{y{\pm}{\delta}y}$ (*). Here, cube-octahedral sites are represented in braces, while quasioctahedral ones with proper octahedral (Y, Cul), square (Cu2) and triangular (CO$_3$) configuration are shown in square brackets. The formula (*) was confirmed by full-profile Rietveld refinement based on X-ray diffraction data of YBa$_{5}$Cu$_2$O$_y$ (1-5-2 phase). Homogeneity region limits of the phase (*) at 96$0^{\circ}C$ in air were determined to be -0.33$\leq$x$\leq$1.80, 0.33$\leq$z$\leq$2.00, 0$\leq$n$\leq$3.

• Ocean and Polar Research
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• v.26 no.2
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• pp.231-243
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• 2004

Sequential extraction was carried out on twenty two subsamples of three ferromanganese crusts from three seamounts (Lemkein, Lomilik, and Litakpooki) near the Marshall Islands in the western Pacific. The extraction was designed to fractionate Fe-Mn crust forming elements into low defined groups: (1) exchangeable and carbornate, (2) Mn-oxide, (3) Fe-oxyhyd.oxide, and (4) residual fraction. X-ray diffraction result shows that target material were well removed by each extraction step except for CFA in phosphatized crusts generation. According to chemical analysis of each leachate, most of elements in the Fe-Mn crusts are bound with two major phases. Mn, Ba, Co, Ni, Zn, (Fe, Sr, Cu, and V) are strongly bounded with Mn-oxide $({\delta}-MnO_2)$ phase, whereas Fe, Ti, Zr, Mo, Pb, Al, Cu,(V, P, and Zn) show chemical affinity with Fe-oxyhydroxide phase. This result indicates that significant amount of Al, Ti, and Zr can not be explained by detrital origin. Ca, Mg, K, and Sr mainly occur as exchangeable elements and/or carbonate phase. Outermost layer 1 and inner layer 2 which are both young crusts generations are similar in chemical speciations of elements. However, some of Fe-oxyhydroxide bounded elements (Pb, Y, Mo, Ba, Al, and V) in phosphatized innermost layer 3 are released during phosphatization and incorporated into phosphate (Pb, Y, Mo, and Ba) or Mn-oxide phase (Al and V). Our sequential extraction results reveal that chemical speciations of elements in the hydrogenetic crusts are more or less different from interelemental relationship calculated by statistical method based on bulk chemistry.