• Journal of Electrochemical Science and Technology
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• v.6 no.4
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• pp.121-130
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• 2015

The micro emulsion method has been successfully used for preparing perovskite LaCoO₃ with uniform, fine-shaped nanoparticles showing high activity as electro catalysts in oxygen reduction reactions (ORRs). They are, therefore, promising candidates for the air-cathode in metal-air rechargeable batteries. Since the activity of a catalyst is highly dependent on its specific surface area, nanoparticles of the perovskite catalyst are desirable for catalyzing both oxygen reduction and evolution reactions. Herein, LaCoO₃ powder was also prepared by sol-gel method for comparison, with a broad particle distribution and high agglomeration. The electro catalytic properties of LaCoO₃ and LaCoO₃-carbon Super P mixture layers toward the ORR were studied comparatively using the rotating disk electrode technique in 0.1 M KOH electrolyte to elucidate the effect of carbon Super P. Koutecky-Levich theory was applied to acquire the overall electron transfer number (n) during the ORR, calculated to be ~3.74 for the LaCoO₃-Super P mixture, quite close to the theoretical value (4.0), and ~2.7 for carbon-free LaCoO₃. A synergistic effect toward the ORR is observed when carbon is present in the LaCoO₃ layer. Carbon is assumed to be more than an additive, enhancing the electronic conductivity of the oxide catalyst. It is suggested that ORRs, catalyzed by the LaCoO₃-Super P mixture, are dominated by a 2+2-electron transfer pathway to form the final, hydroxyl ion product.

• Ceramist
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• v.23 no.2
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• pp.211-230
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• 2020

Perovskite-type oxides with the nominal composition of ABO₃ can exsolve the B-site transition metal upon the controlled reduction. In this exsolution process, the transition metal emerges from the oxide lattice and migrates to the surface at which it forms catalytically active nanoparticles. The exsolved nanoparticles can recover back to the bulk lattice under oxidation treatment. This unique regeneration character by the redox treatment provides uniformly dispersed noble metal nanoparticles. Therefore, the conventional problem of traditional impregnated metal/support, i.e., sintering during reaction, can be effectively avoided by using the exsolution phenomenon. In this regard, the catalysts using the exsolution strategy have been well studied for a wide range of applications in energy conversion and storage devices such as solid oxide fuel cells and electrolysis cells (SOFCs and SOECs) because of its high thermal and chemical stability. On the other hand, although this exsolution strategy can also be applied to gas phase reaction catalysts, it has seldomly been reviewed. Here, we thus review recent applications of the exsolution catalysts to the gas phase reactions from the aspects of experimental measurements, where various functions of the exsolved particles were utilized. We also review non-perovskite type metal oxides that might have exolution phenomenon to provide more possibilities to develop higher efficient catalysts.

• Journal of Electrochemical Science and Technology
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• v.10 no.3
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• pp.335-343
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• 2019

In this study, $Sr_2Ni_{1.8}Mo_{0.2}O_{6-{\delta}}$ (SNM) with a double perovskite structure was investigated as an alternative anode for use in the $CH_4$ fuel in solid oxide fuel cells. SNM demonstrates a double perovskite phase over $600^{\circ}C$ and marginal crystallization at higher temperatures. The Ni nanoparticles were exsolved from the SNM anode during the fabrication process. As the SNM anode demonstrates poor electrochemical and electro-catalytic properties in the $H_2$ and $CH_4$ fuels, it was modified by applying a samarium-doped ceria (SDC) coating on its surface to improve the cell performance. As a result of this SDC modification, the cell performance improved from $39.4mW/cm^2$ to $117.7mW/cm^2$ in $H_2$ and from $15.9mW/cm^2$ to $66.6mW/cm^2$ in $CH_4$ at $850^{\circ}C$. The mixed ionic and electronic conductive property of the SDC provided electrochemical oxidation sites that are beyond the triple boundary phase sites in the SNM anode. In addition, the carbon deposition on the SDC thin layer was minimized due to the SDC's excellent oxygen ion conductivity.

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.718-722
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• 2017

We have investigated the photocatalytic activity for the decomposition of methyl orange on the pure $LaCoO_3$ and metal ion doped $LaCoO_3$ perovskite-typeoxides prepared using microwave process. In the case of pure $LaCoO_3$ and cesium ion doped $LaCoO_3$ catalysts, the formation of the perovskite crystalline phase was confirmed regardless of the preparation method. From the results of UV-Vis DRS, the pure $LaCoO_3$ and cesium ion doped $LaCoO_3$ catalysts have the similar absorption spectrum up to visible region. The chemisorbed oxygen plays an important role on the photocatalytic decomposition of methyl orange and the higher the contents of chemisorbed oxygen, the better performance of photocatalyst.

• Journal of Electrochemical Science and Technology
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• v.9 no.2
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• pp.118-125
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• 2018

Herein we report on the selective synthesis and direct growth of nanostructures using an aqueous chemical growth route. Specifically, Al-doped ZnO (AZO) nanoflakes (NFs) are vertically grown on indium tin oxide (ITO) coated flexible polyethylene terephthalate (PET) sheets at low temperature and ambient environment. The morphological, optical, and electrical properties of the NFs are investigated as a function of the Al content. Furthermore, these AZO-NFs are integrated into perovskite solar devices as the electron transport layer (ETL) and the fabricated devices are tested for photovoltaic performance. It was determined that the doping of AZO-NFs significantly increases the performance metrics of the solar cells, mainly by increasing the short-circuit current of the devices. The observed enhancement is primarily attributed to the improved conductivity of the doped AZO-NF, which facilitates charge separation and reduces recombination. Further, our flexible solar cells fabricated through this low temperature process demonstrate an acceptable reproducibility and stability when exposed to a mechanical bending test.

• Bulletin of the Korean Chemical Society
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• v.6 no.6
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• pp.344-347
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• 1985

Perovskite type oxides of $SrTiO_3,SrZrO_3,and\;SrTi_{1-x}Zr_xO_3$ have been systematically synthesized at $1250^{\circ}C$and $1550^{\circ}C$ with specimens containing additions of up to x=0.9 of zirconium by solid state reactions and characterized by X-ray diffraction. X-ray diffraction studies showed that the compound $SrTi_{1-x}Zr_xO_3$ has cubic structure. The lattice paramters of $SrTi_{1-x}Zr_xO_3$ solid solutions obey the Vegard's law and fairly large increase in volume can acompany the formation of this solution with increasing Zr content(X). Assuming the lattice constants of perovskite type compounds $A(B_{1-x}B'_x)O_3$where $B_{1-x}B'_x$ is $Ti_{1-x}Zr_x$, to be a linear function of the ionic radii of B and B' ions, the disordered ion pair of $Ti^{4+}$and $Zr^{4+}$ was verified from the lattice constants of a series compounds varying x=0,0.05, 0.25, 0.5, 0.75, 0.9, and 1.0 with known isovalent pairs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.1
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• pp.24-30
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• 2003

The preparation of $PbTiO_3$ powder was carried out using the oxide starting material by hydrothermal method. The powder of a crystalline phase with perovskite structure was synthesized. The optimum conditions for the preparation of powder were as follows; hydrothermal solvent; 8M-KOH or 8M-NaOH, reaction temperature; 250~$270^{\circ}C$, run time; 10 h. The ,shape of synthesized powders were well developed crystalline faces with specific surface area of about 2.3 $\textrm m^2$/g in KOH solution and about 5.0 $\textrm m^2$/g in NaOH solution. The cell parameters of powder were a = 3.90$\AA$, c = 4.14 $\AA$ and cell volume was 57.30 $\AA^3$. The cell ratio (c/a) of powder was the same as the theoretical ratio with c/a = 1.06 and the phase transition temperature(Tc) of the powders was about $470^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.36 no.10
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• pp.1056-1061
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• 1999

Phase formation and oxygen ion conduction of La(Ba)Ga(Mg)O3-$\delta$ system was studied, BaLaGa3O7 and BaLaGaO4 formed as a secondary phase above the solubility limit of Ba2+ in La3+ sites. The oxygen ionic conductivity of La(Ba)Ga(Mg)O3-$\delta$ was 0.1 S/cm 80$0^{\circ}C$ The activation energy of the oxygen ion conduction was dependent on temperature. This value was higher at low temperature than at high temperature.

• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1443-1448
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• 1994

Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 solid solution was formed by mixed-oxide method. The phase during formation was analysed by XRD and formation mechanism was investigated. While heat-treating Pb(Mg1/3Nb2/3)O3 composition, the first, Pb2Nb2O7 and Pb3Nb2O8 pyrochlore phases are formed, and finally Pb(Mg1/3Nb2/3)O3 perovskite phase with containing Pb3Nb4O13 pyrochlore phase is obtained at 80$0^{\circ}C$. When Pb(Mg1/3Nb2/3)O3 composition is modified with PbTiO3 which have strong ionic bonding and high tolerance factor, the amount of pyrochlore phase is decreased by increasing of stability in perovskite structure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.10
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• pp.870-875
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• 2002

Ba(Zn$_1$-xCox)TaO$_3$[BZCT] ceramics were Prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of 1450∼1550$\^{C}$ for 5 hr in air. The crystal structure of BZCT ceramics was investigated by the XRD. The microstructure of the specimens were observed by SEM. The structural properties of BZCT specimens were investigated as a function of composition and sintering temperature. All BZCT ceramics sintered over 1550$\^{C}$ were showed a polycrystalline complek perovskite structure without second phases and any unreacted materials. The density of BZCT (70/30) specimen sintered at 1550$\^{C}$ was 6.31g/㎤. In the case of the BZCT(70/30) ceramics sintered at 1550$\^{C}$ for 5 hours, dielectric constant, qualify factor and temperature coefficient of resonant frequency for microwave dielectrics application were a good value of 29, 16,468 at 10㎓ and -4.4 ppm/$\^{C}$, respectively.