• 한국전기전자재료학회논문지
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• 제25권5호
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• pp.392-397
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• 2012

In the $(La_{0.8}Ca_{0.2})(Cr_{0.9}Co_{0.1})O_3$ (LCCC), which has been using as interconnector materials in SOFC, Al ions were substituted for Co because ionic radius of Al is similar to that of Co. Because of the almost identical ionic radius of Al and Co, the substitution was not thought to be affect the tolerance factor of LCCC, and the densification behavior, high temperature electrical conductivity and thermal expansion coefficient were examined as a function of Al concentration. In the cases of the x= 0 and x= 0.02 in $(La_{0.8}Ca_{0.2})(Cr_{0.9}Co_{0.1-x}Al_x)O_3$ (x= 0~0.1), the samples showed the relative densities above ${\geq}95%$ when those were sintered at ${\geq}1,350^{\circ}C$. In the case of the $x{\geq}0.06$ the sintered density deteriorated greatly at lower sintering temperatures. High temperature electrical conductivity of the samples decreased as the content of Al increased. Since the valence state of Al ion is unchangeable, while Cr or Co ions contribute to the electrical conduction by changing those valence states, Al substitution resulted in the decreased electrical conductivity. Al doping of LCCC was an effective way of decreasing the thermal expansion coefficient (TEC).

• 한국분말재료학회지
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• 제12권4호
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• pp.266-272
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• 2005

Transition metal ions($Ni^{2+}$, $Cr^{3+}$ and $V^{5+}$) doped $TiO_2$ nanostructured powders were synthesized by mechanical alloying(MA) to shift the adsorption threshold into the visible light region. The synthesized powders were characterized by XRD, SEM, TEM and BET for structural analysis, UV-Vis and photoluminescence spectrum for the optical study. Also, photocatalytic abilities were evaluated by decomposition of 4-chlorophenol(4CP) under ultraviolet and visible light irradiations. Optical studies showed that the absorption wavelength of transition metal ions doped $TiO_2$ powders moved to visible light range, which was believed to be induced by the energy level change due to the doping. Among the prepared $TiO_2$ powders, $NiO^{2+}$ doped $TiO_2$ powders, showed excellent photooxidative ability in 4CP decomposition.

• 한국진공학회지
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• 제15권5호
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• pp.534-540
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• 2006

$V_2O_3$, $VO_2$, $V_2O_5$ 박막들이 하나의 선구 용액으로부터 다양한 후열처리 조건을 통하여 제작될 수 있었다. 진공 중 후열처리 시 rhombohedral 구조의 $V_2O_3$ 박막이 형성되어졌고, 공기 중 후열처리 시 orthorhombic 구조의 $V_2O_5$ 박막을 얻을 수 있었다. Monoclinic 구조의 $VO_2$ 박막은 진공 후열처리 중 $O_2$ 가스를 공급함으로써 제작될 수 있었다. $V_2O_3$ 박막이 상온에서 도체적 특성을 보이는 반면, $V_2O_5$, $VO_2$ 박막은 반도체적 성질을 지니고 있음을 전기적, 광학적 특성 조사를 통하여 알 수 있었다. 크롬(Cr)이 도핑됨에 따라 $VO_2$ 박막은 그 전기전도성이 n-type에서 p-type으로 변화하였고 비저항이 감소되는 결과를 나타내었다. 또한, 크롬 도핑된 $VO_2$ 박막은 orthorhombic 구조를 나타내었다. 이와 같은 바나듐 옥사이드 박막들에서 관측된 광학적 흡수 구조들은 O 2p 에서 V 3d 밴드로의 전이에 의한 것으로 해석되어진다. 바나듐 이온의 $t_{2g}$ 상태와 $e_g$ 상태 사이의 결정장 갈라짐(crystal-field splitting)은 $V_2O_5$와 $VO_2$에 대해서 각각 1.5 및 1.0 eV로 해석된다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.80.1-80.1
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• 2010

A strontium titanate ($SrTiO_3$)-based material with a perovskite structure is considered to be one of the promising alternatives to $LaCrO_3$-based materials since $SrTiO_3$ perovskite shows a high chemical stability under both oxidizing and reducing atmospheres at high temperatures. $SrTiO_3$ materials exhibit an n-type semiconducting behavior when it is donor-doped and/or exposed to a reducing atmosphere. In this work, $Sr_{1-x}La_xTi_{1-y}M_yO_3$ materials doped with $La^{3+}$ in A-sites and aliovalent transition metal ions ($M^{n+}$) in B-sites were synthesized by the modified Pechini method. The X-ray diffraction analysis indicated that the materials synthesized by the Pechini process exhibited a single curbic perovskite-type structure without any impurity phases, and are tolerant, to some extent, to cation doping. The sintering behaviors of $Sr_{1-x}La_xTi_{1-y}M_yO_3$ in $H_2/N_2$ and air were characterized by dilatometry and microstructural observations. The electrical conduction mechanism and the dopant effect are discussed based on the defect structures and the electrical conductivities measured at various oxygen partial pressures and temperatures.

• 한국분말재료학회지
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• 제12권6호
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• pp.399-405
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• 2005

Nanopowders of titanium dioxide $(TiO_2)$ incorporating the transition metal element(s) were synthesized by flame synthesis method. Single element among Fe(III), Cr(III), and Zn(II) was doped into the interior of $TiO_2$ crystal; bimetal doping of Fe and Zn was also made. The characteristics of transition-metal-doped $TiO_2$ nanopowders in the particle feature, crystallography and electronic structures were determined with various analytical tools. The chemical bond of Fe-O-Zn was confirmed to exist in the bimetal-doped $TiO_2$ nanopowders incorporating Fe-Zn. The transition element incorporated in the $TiO_2$ was attributed to affect both Ti 3d orbital and O 2p orbital by NEXAFS measurement. The bimetal-doped $TiO_2$ nanopowder showed light absorption over more wide wavelength range than the single-doped $TiO_2$ nanopowders.

• Current Applied Physics
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• 제18권11호
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• pp.1268-1274
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• 2018

We have investigated the effects of chemical rounding (CR) on the surface passivation and/or antireflection performance of $AlO_{x^-}$ and $AlO_x/SiN_x:H$ stack-passivated pyramid textured $p^+$-emitters with two different boron doping concentrations, and on the performance of bifacial n-PERT Si solar cells with a front pyramid textured $p^+$-emitter. From experimental results, we found that chemical rounding markedly enhances the passivation performance of $AlO_x$ layers on pyramid textured $p^+$-emitters, and the level of performance enhancement strongly depends on boron doping concentration. Meanwhile, chemical rounding increases solar-weighted reflectance ($R_{SW}$) from ~2.5 to ~3.7% for the $AlO_x/SiN_x:H$ stack-passivated pyramid textured $p^+$-emitters after 200-sec chemical rounding. Consequently, compared to non-rounded bifacial n-PERT Si cells, the short circuit current density Jsc of 200-sec-rounded bifacial n-PERT Si cells with ~60 and ${\sim}100{\Omega}/sq$ $p^+$-emitters is reduced by 0.8 and $0.6mA/cm^2$, respectively under front $p^+$-emitter side illumination. However, the loss in the short circuit current density Jsc is fully offset by the increased fill factor FF by 0.8 and 1.5% for the 200-sec-rounded cells with ~60 and ${\im}100{\Omega}/sq$ $p^+$-emitters, respectively. In particular, the cell efficiency of the 200-sec-rounded cells with a ${\sim}100{\Omega}/sq$ $p^+$-emitter is enhanced as a result, compared to that of the non-rounded cells. Based on our results, it could be expected that the cell efficiency of bifacial n-PERT Si cells would be improved without additional complicated and costly processes if chemical rounding and boron doping processes can be properly optimized.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.157-157
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• 2009

$BaTiO_3$를 기본조성으로 하는 PTC 써미스터는 Curie 온도이상에서 저항이 급격히 상승하는 반도성 전자세라믹스로서 degaussing 소자, 정온 발열체, 온도센서, 전류 제한 소자 등 상업적으로 폭넓게 사용되고 있다. 본 소자는 소결온도, 소결 및 열처리 분위기, 불순물, 첨가제 등의 제조공정상의 인자들과 기공률, 결정립 크기 등이 복합적으로 작용하여 PTCR 특성이 크게 영향을 받기 때문에 제조하기에 무척 까다로운 소자로 알려져 있다. 특히 과전류 보호 소자용으로 사용하기 위해서는 상온 비저항을 크게 낮추어야 하며 이에 대한 연구가 계속 진행되고 있다. 따라서 본 연구에서는 SiO2을 0.5~10 at%로 달리한 조성으로 환원 분위기에서 소결하고 공기 중에서 재산화 처리하여 재료의 PTC 특성에 어떠한 영향을 미치는지 분석하였다. 소정의 조성을 선택하여 $1180^{\circ}C{\sim}1240^{\circ}C$에서 2시간 동안 환원분위기에서 소결하고, $800^{\circ}C$에서 1 시간 공기 중에서 재산화 처리한 후 R-T 특성을 측정하여 SiO2 함량에 따른 PTC 특성을 분석하였다. 그 결과 SiO2의 함량이 증가할수록 상온 저항은 낮아지다가 3.0 at% 이상으로 첨가할 경우 급격히 상승하는 경향을 나타내었다. 특히 SiO2를 1.0~3.0 at% 일 때 우수한 PTC 특성을 가졌다. $1180^{\circ}C$에서는 소결 밀도가 낮아 상온 비저항이 크게 높았지만, $1200^{\circ}C{\sim}1220^{\circ}C$에서는 정상 입성장이 나타나면서 일반적인 PTC 특성을 가졌지만, $1240^{\circ}C$ 이상에서는 공정 액상이 형성되어 비정상 입성장이 일어나 상온 비저항이 크게 낮아졌다. 한편 점핑비-log(Rmax/Rmin)는 SiO2 함량이 증가할수록 높아지다가 3.0 at% 이상에서는 낮아짐을 확인하였다.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1300-1309
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• 2023

Simulated debris was synthesized using UO₂, Zr, and stainless steel and a heat treatment method under inert or oxidizing conditions. The primary U solid phase of the debris synthesized at 1473 K under inert conditions was UO₂, whereas a (U, Zr)O₂ solid solution formed at 1873 K. Under oxidizing conditions, a mixture of U₃O₈ and (Fe, Cr)UO₄ phases formed at 1473 K, whereas a (U, Zr)O_2+x solid solution formed at 1873 K. The leaching behavior of the fission products from the simulated debris was evaluated using two methods: the irradiation method, for which fission products were produced via neutron irradiation, and the doping method, for which trace amounts of non-radioactive elements were doped into the debris. The dissolution behavior of U depended on the properties of the debris and aqueous solution for immersion. Cs, Sr, and Ba leached out regardless of the primary solid phases. The leaching of high-valence Eu and Ru ions was suppressed, possibly owing to their solid-solution reaction with or incorporation into the uranium compounds of the simulated debris.