• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.387-392
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• 2007

Thermal conductivities in $La_2Ce_2O_7-Gd_2Ce_2O_7-Y_2Ce_2O_7$ ternary system have been investigated. Pyrochlore phases formed at all ternary compositions and their sinterbilities were decreased with La addition. Thermal conductivities showed a minimum value at $La_2Ce_2O_7$ with moderate increases as $Y^{3+}$ and $Gd^{3+}$ ions replaced $La^{3+}$. Thermal expansion anomaly observed in $La_2Ce_2O_7$, which might be detrimental to TBC application, were suppressed by $Y^{3+}$ and $Gd^{3+}$ additions, with resultant thermal conductivities, $1.3{\sim}1.5 W/mK$ at $1000^{\circ}C$.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.12
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• pp.668-673
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• 2015

Alumina-based catalysts with different Ce loadings were studied in the decomposition of $CF_4$ using microwave heating system. Heating material of microwave system used Silicon Carbide. The crystallographic phases of catalysts were investigated by XRD and decomposition rates of $CF_4$ were examined by GC-TCD. The catalysts of 10 wt% Ce modified $Al_2O_3$ showed higher $CF_4$ decomposition rate than un-modified $Al_2O_3$ for $500^{\circ}C$ reaction temperature. The k value of catalysts shows the order of $Ce(20)/Al_2O_3=Ce(0)/Al_2O_3<Ce(5)/Al_2O_3<Ce(10)/Al_2O_3$. XRD patterns of $Ce(0)/Al_2O_3$ were no difference before and after the reaction and showed $Al_2O_3$ phases. With the increase in Ce loadings, $CeO_2$, $AlF_3$ of XRD peaks was observed. The results was indicated that Ce modifed $Al_2O_3$ than un-modifed $Al_2O_3$ was decreased reaction temperature to $200^{\circ}C$ with same decomposition rate. Also the appropriated cerium sulfate loadings on $Al_2O_3$ were 5~10 wt%.

• Economic and Environmental Geology
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• v.37 no.6 s.169
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• pp.603-612
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• 2004

Pyrochlore is known as one of the most promising materials for the immobilization of radionuclide in high level waste. This study included the synthesis, phase relation and characteristics of $pyrochlore(CaCeZr_xTi_{2-x}O_{7,\;x=0.2\~2.0)$ in the system of Ca-Ce-Zr-Ti-O. Using the CPS(Cold pressing and sintering) method, the mixtures of $CaCO3_,\;CeO_2,\;ZrO_2\;and\;TiO_2$ oxides were pressed, and sintered at $1100\~1600^{\circ}C$ for 20 hours. The optimal synthetic conditions at various compositions were differed from 1300 to $1600^{\circ}C$ Even in the optimal temperatures, pyrochlore or fluorite coexisted with minor amount of perovskite, $CeO_2\;or\;Ce_{0.75}Zr_{0.25}O_2$. It was confirmed that pyrochlore and fluorite structures were stable at $x\leq0.6\;and\;x\geq1.0$, respectively. Especially, the compositions of pyrochlore or fluorite showed non-stoichiometric compositions in that contents of Ca and Ti were more deficient and those of Zr and Ce were more excess than batch compositions with the increase of x value. These characteristics stemmed from the behavior of elements occupied at eight- and six-coordinated site, and then caused the coexistence of perovskite, $CeO_2\;or\;Ce_{0.75}Zr_{0.25}O_2$ along with pyrochlore or fluorite.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.705-712
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• 2000

In this study, the dispersion stability of CeO2 based complex oxide was studied, and density, porosity, and microstructure of green body were investigated using colloid surface chemistry to manufacture the Gd2O3 doped CeO2 solid electrolyte in an aqueous system. To prepare the stable slurry for slip casting, the dispersion stability was examined as a function of pH using ESA(electrokinetic sonic anplitude) analysis. The dynamic mobility of particles was enhanced with anionic and cationic dispersant were added the amount of 0.5wt% respectively, but pH value in slurries didn't move to below 6.0 because of the influence of dopants. This phenomenon also appeared in the CeO2-Y2O3 and CeO2-Sm2O3 systems, so it could be inferred that rare earth dopants such as Gd2O3, Sm2O3 and Y2O3 not only have the similar motion with changing pH in an aqueous system but also can be dissolved in the range of pH 6.0∼6.5. In CeO2-Gd2O3 system, when the anionic dispersant was added the amount of 0.5wt% and pH value in slurries was fixed at 9.5, the green body density was 4.07g/㎤, and the relative density of sintered body was 95.2%. It could be inferred from XRD analysis that Gd3+ substituted into Ce4+ site because there was no free Gd2O3 peak.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.469-472
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• 1999

CeO$_2$ thin films have used in wide applications such as SOI, buffer layer, antirflection coating, and gate dielectric layer. CeO$_2$takes one of the cubic system of fluorite structure and shows similar lattice constant (a=0.541nm) to silicon (a=0.543nm). We investigated CeO$_2$films as buffer layer material for nonvolatile memory device application of a single transistor. Aiming at the single transistor FRAM device with a gate region configuration of PZT/CeO$_2$ /P-Si , this paper focused on CeO$_2$-Si interface properties. CeO$_2$ films were grown on P-type Si(100) substrates by 13.56MHz RF magnetron sputtering system using a 2 inch Ce metal target. To characterize the CeO$_2$ films, we employed an XRD, AFM, C-V, and I-V for structural, surface morphological, and electrical property investigations, respectively. This paper demonstrates the best lattice mismatch as low as 0.2 % and average surface roughness down to 6.8 $\AA$. MIS structure of CeO$_2$ shows that breakdown electric field of 1.2 MV/cm, dielectric constant around 13.6 at growth temperature of 200 $^{\circ}C$, and interface state densities as low as 1.84$\times$10$^{11}$ cm $^{-1}$ eV$^{-1}$ . We probes the material properties of CeO$_2$ films for a buffer layer of FRAM applications.

• Korean Journal of Materials Research
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• v.3 no.3
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• pp.276-281
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• 1993

In order to study the sintering kinetics of the ternery system, U-Ce-O, its shrinkage rate with time and temperature at the Ar atmoshpere were measured by using the dilatometer. At the sintering kinetics of U-Ce-O, sintering rate curve revealed bimodal and the first extreme point at bimodal curve was affected by the $UO_2$ the second one was due to the $CeO_2$. The sintering of $(U, Ce)O_2$ was delayed as increasing the $CeO_2$. At the same lOwt. % content, the highest sintering rate was observed at the $(U, Ce)O_2$ sample ball-milled for 4 hours.

• Clean Technology
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• v.26 no.4
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• pp.286-292
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• 2020

This study confirmed the effect of the Cu/CeO2-X catalyst on the CO oxidation activity at low temperature through the catalyst's structure and reaction characteristics. The catalyst was prepared by the wet impregnation method. Cu/CeO2_X catalysts were manufactured by loading Cu (active metal) using CeO2 (support) formed at different calcination temperatures (300-600 ℃). Manufactured Cu/CeO2_X catalysts were evaluated for the low-temperature activity of carbon monoxide. The Cu/CeO2_300 catalyst showed an activity of 90% at 125 ℃, but the activity gradually decreased as the calcination temperature of the CeO2-X and Cu/CeO2_600 catalysts showed an activity of 65% at 125 ℃. Raman, XRD, H2-TPR, and XPS analysis confirmed the physicochemical properties of the catalysts. Based on the XPS analysis, the lower the calcination temperature of the CeO2 was, the higher the unstable Ce3+ species (non-stoichiometric species) ratio became. The increased Ce3+ species formed a solid solution bond between Cu and CeO2-X, and it was confirmed by the change of the CeO2 peak in Raman analysis and the reduction peak of the solid solution structure in H2-TPR analysis. According to the result, the formation of the solid solution bond between Cu and Ce has been enhanced by the redox properties of the catalysts and by CO oxidation activity at low temperatures.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.112-114
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• 2005

Dispersion stability of the $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles, which was produced by hydrothermal process, was studied in aqueous suspension using ESA (Eletrokinetic Sonic Amplitude). The average particle size of the synthesized $Sm_xCe_{1-x}O_{2-2/x}$ at nanoparticles was about $5{\pm}2nm$. The dispersion and rheological behavior of the $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles aqueous suspension was investigated using $NH_4OH\;and\;HNO_3$ as a disperse agent. The colloidal stability of aqueous suspensions with $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles at different pH values has been investigated by means of zeta potential, average particle size, and the distribution of synthesized $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles. The isoelectric point of the $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles was at pH around 11 and the value of zeta potential was at its maximum near pH 6.5.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.11
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• pp.979-986
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• 2003

Sintering behavior and electrical properties of CeO$_2$ system were investigated as a function of the amount of Gd:$_2$O$_3$, and Sm$_2$O$_3$, addition. Doped CeO$_2$ consisted of a homogeneous solid solution of the cubic fluorite structure within the amount of addition from 0 mol% to 15 mol%. Grain growth rate of Gd$_2$O$_3$-doped CeO$_2$ was much smaller than that of pure CeO$_2$, while densification rate was considerably larger. Thus doped CeO$_2$ showed a higher density than pure CeO$_2$. The electrical conductivity of Ce$_1$-$_{x}$Sm$_{x}$O$_1$-$_{x}$/2 was increased up to x = 0.2. However, with further increasing dopant concentrations, the magnitude of the conductivity was found to decrease remarkably. The ionic conductivity value obtained at $700^{\circ}C$ for 10 mol% Sm$_2$O$_3$-doped CeO$_2$ electrolyte was 4.6${\times}$10$^{-2}$ S$.$$cm^{-1}$ /.EX> /.

• Journal of the Korean Ceramic Society
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• v.30 no.11
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• pp.941-948
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• 1993

The powder mixture of Si3N4-AlN-Y2O3, Si3N4-AlN-CeO2 and Si3N4-AlN-Y2O3-CeO2 system was hot-pressed at 175$0^{\circ}C$ for 2h in N2 to prepare $\alpha$-Sialon ceramics. The mechanical property and oxidation behaviour of the prepared $\alpha$-Sialon ceramics were investigated. At 120$0^{\circ}C$, oxidation resistance was best for the Y2O3 added $\alpha$-Sialon ceramics and oxidation rate increased when the amount of CeO2 increased. But when the mixture of Y2O3 and CeO2 added $\alpha$-Sialon ceramics showed a good oxidation resistance. Fracture toughness of (Y2O3＋CeO2) added $\alpha$-Sialon ceramics was higher than Y2O3 added $\alpha$-Sialon ceramics.