• Title/Summary/Keyword: CoO doping

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Preparation of CdS-pillared $H_4Nb_6O_7$ and Photochemical Reduction of Nitrate under Visible Light Irradiation

  • Tawkaew, Sittinun;Fujishiro, Yoshinobu;Uchida, Satoshi;Sato, Tsugio
    • The Korean Journal of Ceramics
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    • v.6 no.1
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    • pp.43-46
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    • 2000
  • $H_4Nb_6/O_{17}$/CdS nanocomposites which intercalated CdS particles, less than 0.8nm thickness, in the interlayer of $H_4Nb_6/O_{17}$ were prepared by the successive ion exchange reactions of $H_4Nb_6/O_{17}$ with $Cd^{2+}$ and $C_3H_7NH_3_+$, followed by the reaction with $H_2S$ gas. $H_4Nb_6/O_{17}$/CdS photocatalytically reduced $NO_3$ ̄ to $NO_2$ ̄ and $NH_3$in the presence of sacrificial hole acceptor such as methanol under visible light irradiation (wavelength>400nm), although unsupported CdS showed no noticeable photocatalytic activity for $NO_3$ ̄ reduction. The catalytic activity of $H_4Nb_6/O_{17}$/CdS greatly enhanced with co-doping of Pt particles in the interlayer.

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Rational Design of Binder-Free Fe-Doped CuCo(OH)2 Nanosheets for High-Performance Water Oxidation

  • Patil, Komal;Jang, Su Young;Kim, Jin Hyeok
    • Korean Journal of Materials Research
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    • v.32 no.5
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    • pp.237-242
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    • 2022
  • Designing and producing a low-cost, high-current-density electrode with good electrocatalytic activity for the oxygen evolution reaction (OER) is still a major challenge for the industrial hydrogen energy economy. In this study, nanostructured Fe-doped CuCo(OH)2 was discovered to be a precedent electrocatalyst for OER with low overpotential, low Tafel slope, good durability, and high electrochemically active surface sites at reduced mass loadings. Fe-doped CuCo(OH)2 nanosheets are made using a hydrothermal synthesis process. These nanosheets are clumped together to form a highly open hierarchical structure. When used as an electrocatalyst, the Fe-doped CuCo(OH)2 nanosheets required an overpotential of 260 mV to reach a current density of 50 mA cm-2. Also, it showed a small Tafel slope of 72.9 mV dec-1, and superior stability while catalyzing the generation of O2 continuously for 20 hours. The Fe-doped CuCo(OH)2 was found to have a large number of active sites which provide hierarchical and stable transfer routes for both electrolyte ions and electrons, resulting in exceptional OER performance.

Magnetic and Microwave Absorbing Properties of M-type Hexagonal Ferrites Substituted by Ru-Co(BaFe12-2xRuxCoxO19) (Ru-Co가 치환된 M-형 육방정 페라이트(BaFe12-2xRuxCoxO19)의 자기적 성질 및 전파흡수 특성)

  • Cho, Han-Shin;Kim, Sung-Soo
    • Journal of the Korean Magnetics Society
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    • v.18 no.4
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    • pp.136-141
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    • 2008
  • In this study, the magnetic(static and high-frequency) and microwave absorbing properties have been investigated in Ru-Co substituted M-hexaferrites($BaFe_{12-2x}Ru_xCo_xO_{19}$). The powders and sintered specimens were prepared by conventional ceramic processing technique. With the calcined powders, the composite specimens were prepared using the silicone rubber as a matrix material. The substitution ratio of Ru-Co to obtain in-plane magnetic anisotropy, thus having the minimum coercivity, is much smaller (about x=0.3) than the previously reported Ti-Co substituted specimen. Owing to this low substitution, the specimen has a large value of saturation magnetization($M_s$=65 emu/g). Ferromagnetic resonance behavior and microwave absorbing frequency band is strongly influnced by the coercvity which can be controlled by Ru-Co substitution ratio. It is found that the M-hexaferrites with planar magnetic anisotropy by doping Ru-Co in both sintered and composite form have superior microwave absorbing properties in GHz frequency range.

Luminescence Characteristics of Mg2+·Ba2+ Co-Doped Sr2SiO4:Eu Yellow Phosphor for Light Emitting Diodes (LED용Mg2+·Ba2+Co-Doped Sr2SiO4:Eu 노란색 형광체의 발광특성)

  • Choi, Kyoung-Jae;Jee, Soon-Duk;Kim, Chang-Hae;Lee, Sang-Hyuk;Kim, Ho-Kun
    • Journal of the Korean Ceramic Society
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    • v.44 no.3 s.298
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    • pp.147-151
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    • 2007
  • An improvement for the efficiency of the $Sr_{2}SiO_{4}:Eu$ yellow phosphor under the $450{\sim}470\;nm$ excitation range have been achieved by adding the co-doping element ($Mg^{2+}\;and\;Ba^{2+}$) in the host. White LEDs were fabricated through an integration of an blue (InGaN) chip (${\lambda}_{cm}=450\;nm$) and a blend of two phosphors ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) in a single package. The InGaN-based two phosphor blends ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) LEDs showed three bands at 450 nm, 550 nm and 640 nm, respectively. The 450 nm emission band was due to a radiative recombination from an InGaN active layer. This 450 nm emission was used as an optical transition of the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor. As a consequence of a preparation of white LEDs using the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor yellow phosphor and CaS:Eu red phosphor, the highest luminescence efficiency was obtained at the 0.03 mol $Ba^{2+}$ concentration. At this time, the white LEDs showed the CCT (5300 K), CRI (89.9) and luminous efficacy (17.34 lm/W).

Study of Electrical Conductivity of BaZr0.85-xPdxY0.15O3-δ/ Carbonates Composite Materials (BaZr0.85-xPdxY0.15O3-δ/ Carbonates 복합전도체 전기적 특성 연구)

  • Park, Ka-Young;Baek, Seung-Seok;Park, Jun-Young
    • Journal of the Korean Ceramic Society
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    • v.51 no.4
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    • pp.283-288
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    • 2014
  • PdO-doped $BaZr_{0.85}Y_{0.15}O_{3-\delta}$ (BZPY) proton conductors have been proposed as applicable for intermediate temperature electrolytes for protonic ceramic fuel cells (PCFCs) because the PdO doping is effective for improving the proton conductivity of $BaZr_{0.85}Y_{0.15}O_{3-\delta}$ (BZY) with high affinity for hydrogen. In order to further improve the conductivity of BZPY, two-phase composite electrolytes consisting of a BZPY and molten carbonate were designed. Dense BZPY-based composite electrolytes were fabricated after sintering at $670^{\circ}C$ for 4 h, since molten carbonates fill the grain boundary of the porous BZPY matrix. Furthermore, BZPY/$(Li-0.5Na)_2CO_3$ composites show a significantly enhanced protonic conductivity at intermediate temperatures. This may be because easy proton transport is possible through the interface of the carbonate and oxide phase.

A study on the structural and electric properties of fluorinated $YBa_2Cu_3O_{7-y}$ (불소화된 $YBa_2Cu_3O_{7-y}$ 초전도체의 구조적, 전기적 성질에 관한 연구)

  • 김재욱;김채옥
    • Electrical & Electronic Materials
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    • v.9 no.4
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    • pp.404-409
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    • 1996
  • The structural and electric properties of $Y_{1-x}$YbF$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-y}$(x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) have been investigated by using XRD(X-ray diffraction), TMA(thennomechanical analysis), NMR(nuclear magnetic resonance) analysis and four probe method. $Y_{1-x}$YbF$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-y}$ samples were prepared by conventional solid-state reaction method using $Y_{2}$O$_{3}$, BaCO$_{3}$, CuO and YbF$_{3}$ power. TMA and high temperature XRD results shows that orthorhombic to tetragonal phase transition occurs in the unfluorinated 1-2-3 sample while the phase change is not observed in the fluorinated 1-2-3 samples. Superconducting transition temperature(T$_{c}$) increases with increasing YbF$_{3}$ content ; T$_{c}$, of the sample reaching maximum of 102K for x=0.3, and then decreases with further increasing YbF$_{3}$ content. The structural analysis and T$_{c}$ results shows that the fluorine doping stabilize the orthorhombic phase, together with the increase in T$_{c}$.}$ c/.TEX> c/.

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Fast Responding Gas Sensors Using Sb-Doped SnO2 Nanowire Networks (Sb-첨가 SnO2 나노선 네트워크를 이용한 고속응답 가스센서)

  • Kwak, Chang-Hoon;Woo, Hyung-Sik;Lee, Jong-Heun
    • Journal of Sensor Science and Technology
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    • v.22 no.4
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    • pp.302-307
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    • 2013
  • The Sb-doped $SnO_2$ nanowire network sensors were prepared by thermal evaporation of the mixtures between tin and antimony powders. Pure $SnO_2$ nanowire networks showed high sensor resistance in air ($99M{\Omega}$), similar gas responses to 4 diffferent gases (5 ppm $C_2H_5OH$, CO, $H_2$, and trimethylamine), and very sluggish recovery speed (90% recovery time > 800 s). In contrast, 2 wt% Sb-doped $SnO_2$ showed the selective detection toward $C_2H_5OH$ and trimethylamine, relatively low resistance ($176k{\Omega}$) for facile measurement, and ultrafast recovery speed (90% recovery times: 6 - 18 s). The change of gas sensing charactersitics by Sb doping was discussed in relation to gas sensing mechanism.

Synthesis and high Temperature properties of Li$_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$spinel prepared by oxalate precipitation (Oxalate 침전법의 의한 Li$_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$spinel의 합성 및 고온특성)

  • 김세호;이병우
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.3
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    • pp.239-244
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    • 2000
  • Synthesis and high temperature phase stability of $_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$(0$\leq$x$\leq$0.2,y=0,1/9,1/6) spinel, both the excess lithium and cobalt added, have been studied. The spinel was prepared by oxalate precipitation method as the wet chemical process. Oxalate derived spinel was synthesized by heating of precipitates at temperature lower than $600^{\circ}C$. As a result of the TG-DTA and XRD analysis of prepared and quenched powders, it was found that reversible phase transitions started at temperatures $T_1$, $T_2$$T_{2'}$. The transitions involved weight (oxygen) loss and gain during heating and cooling. The effects of Li excess and Co doping on the spinel lattice constant, phase stability and transition temperatures of the prepared powders are investigated. This study would provide important data for determining the spinel preparation process such as synthesis temperature and cooling speed.

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Fabrication of Fe-doped LaGaO3 Perovskite Mixed Conductor and Improvement of Oxygen Permeability by Screen Printing Coating (Fe가 Doping 된 LaGaO3 폐롭스카이트 혼합 전도체의 제조 및 코팅에 따른 산소투과 성능 향상)

  • Lim, Kyung Tae;Cho, Tong Lae;Lee, Kee Sung;Woo, Sang Kuk;Park, Kee Bae;Kim, Jong Won
    • Transactions of the Korean hydrogen and new energy society
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    • v.12 no.2
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    • pp.137-146
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    • 2001
  • 고상 반응법을 이용하여 $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-{\delta}}$ 분말을 합성하고 혼합전도체 분리막을 소결하여 제조하였다. 제조된 분리막은 $LaGaO_3$에 일치하는 폐롭스카이트 결정구조를 나타내었으며 95% 이상의 높은 상대밀도를 나타내었다. 스크린 프린팅 방법으로 $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ 후막을 disk의 양 표면에 코팅하였으며 코팅 막은 비교적 치밀한 미세구조를 나타내었다. 코팅되지 않은 분리막과 코팅된 분리막의 산소투과 성능을 비교 실험한 결과 $850^{\circ}C$에서 동일한 두께의 코팅된 분리막의 정상상태 산소 투과 유속이 $0.7{m{\ell}}/min.cm^2$ 정도로 코팅되지 않은 분리막에 비해 약 2~3배로 높게 나타났다.

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