• 한국자기학회지
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• 제18권6호
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• pp.217-220
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• 2008

Rare-earth iron oxide $ErFe_2O_4$의 다결정체 시료의 자기적 특성을 연구하였다. 단일상의 다결정체 $ErFe_2O_4$ 시료를 CO/$CO_2$ gas 분위기에서 고체상태반응법으로 합성하였다. X-ray diffraction 측정을 통해 $ErFe_2O_4$ 시료는 space group R3m Rhombohedral 구조를 가지며, 온도에 의존하는 magnetization 측정을 통해 250 K에서는 자기적 전이가, 220 K에서는 구조적 전이가 일어나는 2단계 상전이 현상을 확인하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제21권4호
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• pp.1-5
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• 2019

We investigated the effect of Fe₃O₄ addition on the critical temperature of (Bi, Pb)-2223 polycrystalline samples. Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ + x wt. % Fe₃O₄ (x = 0.0, 0.2, 0.4, 0.6, and 0.8) samples were prepared by using a solid-state reaction method. The analysis of X-ray diffraction data indicates that as Fe₃O₄ is added, dominant phase of the sample changes from Bi-2223 to Bi-2212 with an increasing Bi-2201 phase. The transition temperature of the samples drastically decreased with the Fe₃O₄ addition. The resistance data of samples with x = 0.2 and 0.4 showed a double transition indicating a coexistence of Bi-2223 and Bi-2212 phase while the samples with x = 0.6 and 0.8 showed a single transition with a semiconducting behavior. This phase transition may originate from changes in local structure of the Bi-2223 system by Fe₃O₄ addition. Analysis of the pair distribution function of the Cu-O pair in the CuO₂ plane calculated from extended X-ray absorption fine structure data revealed that the oxygen coordination of copper ion changes from CuO₄ planar type (x = 0.0 - 0.4) to CuO₅ pyramidal type (x = 0.6, 0.8). The correlated Debye-Waller factor, providing information on the atomic disorder within the CuO₂ plane, shows an inverse relation to the coordination number. These results indicate that addition of Fe₃O₄ changes the oxygen distribution around Cu in the CuO₂ plane, causing a phase transition from Bi-2223 to more stable Bi-2212/Bi-2201 phases.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.311-314
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• 1998

The effects of the additions of transition metal oxides on ZrO$_2$ - Y$_2$O$_3$ (Y$_2$O$_3$ - containing tetragonal zirconia polycrystals : Y-TZP) system has been studied by investigating fracture toughness and phase stability of the sintered specimens. In the specimens sintered at 1450$^{\circ}C$ for 2hrs in air the phase transformation from tetragonal to monoclinic was observed. The ratios of monoclinic phase to tetragonal phase were changed with the additions of CoO, Fe$_2$O$_3$ and MnO$_2$, respectively, from 0.00 to 8.00wt%. The fracture toughness was increased with increasing the monoclinic to tetragonal phase ratio and was maximum at the ratio of about 18%. However, the hardness was decreased with increasing the ratio. The additions of CoO, Fe$_2$O$_3$ and MnO$_2$ together into Y-TZP resulted in more complex behaviors of fracture toughness and hardness. The specimen with the additions of 1.5wt% Fe$_2$O$_3$, 3.0wt% Al$_2$O$_3$ and 1.5wt% CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$\^$$\frac{1}{2}$/ and Vickers hardness of 1201kgf/mm$^2$.

• Bulletin of the Korean Chemical Society
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• 제28권8호
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• pp.1273-1279
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• 2007

The NiSO4 supported on Fe2O3 catalysts were prepared by the impregnation method. No diffraction line of nickel sulfate was observed up to 30 wt %, indicating good dispersion of nickel sulfate on the surface of Fe2O3. The addition of nickel sulfate to Fe2O3 shifted the phase transition of Fe2O3 (from amorphous to hematite) to higher temperatures because of the interaction between nickel sulfate and Fe2O3. 20-NiSO4/Fe2O3 containing 20 wt % of NiSO4 and calcined at 500 oC exhibited a maximum catalytic activity for ethylene dimerization. The initial product of ethylene dimerization was found to be 1-butene and the initially produced 1-butene was also isomerized to 2-butene during the reaction. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method.

• 한국결정학회지
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• 제13권3_4호
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• pp.165-171
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• 2002

고상반응법에 의해 합성된 분말을 $1100^{\circ}C$에서 소결함으로써 밀도가 $9.3g/cm^3$이고 평균입경이 $5.1{\pm}1.2{\mu}$인 $Pb(Fe_{1/2}Ta_{1/2})O_3$를 단일상으로 합성하였다. (공간군: Pm3m) $-150{\sim}50^{\circ}C$에서 측정된 비유전율은 인가전압의 주파수가 1kHz일 때 $-41^{\circ}C$에서 비유전율이 3100으로 최대값을 가지고 유전완화(dielectric relaxation)현상 및 완만한 상전이(diffuse phase transition, DPT)가 뚜렷하게 관찰되는 전형적인 완화형 강유전특성을 보였으며 소결후 $1000^{\circ}C$에서의 열처리 시간이 증가함 에 따라 상전이의 완만화도는 감소하여 정상 강유전체화 하였다. 한편, 소결직후 $Fe^{3+}$와 $Ta^{5+}$ 이온은 투과전자현미경으로도 검출할 수 없는 정도의 단거리 영역에서 화학양론적으로 1 : 1 질서 배열하고 있으며 이러한 B자리 양이온의 질서배열은 열처리 시간이 증가함에 따라 강화됨을 라만분광법으로 확인하였다. 소결직후 $Pb(Fe^{12}Ta_{1/2})O_3$센서의 완화형 강유전특성은 B자리 양이온의 화학양론적 1:1 단거리 질서배열구조와, 열처리한 $Pb(Fe_{1/2}TA_{1/2})O_3$에서의 완화형 강유전특성 감소는 열처리에 따라 강화된 화학양론적 1:1 단거리 질서배열구조와 연관지을 수 있었다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2000년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.41-41
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• 2000

• E2M - 전기 전자와 첨단 소재
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• 제8권2호
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• pp.190-195
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• 1995

Temperature dependences of the dielectric constant K(T), remanent polarization $P_{r}$, (T), effective birefringence overbar .DELTA.n(T), transmitted light intensity and quadratic electro optic coefficient R(T) of the two-stage sintered xBa(L $a_{1}$2/N $b_{1}$2/) $O_{3}$-(1-x)Pb(Z $r_{y}$ $Ti_{1-y}$) $O_{3}$(x=0.085, 0.09, 0.40.leq.y.leq.0.70) ceramics were investigated. Increasing the PbZr $O_{3}$ contents, the crystal structure of a specimen was changed from a tetragonal phase to a rhombohedral and cubic phase, and the phase transition was showed a diffuse phase transition(DPT) characteristics. In the compositions which located on the PE-FE phase boundary, the discrepancy was observed between the Curie temperature and temperature which a microscopic polarization and effective birefringence were disappeared.red.d.

• Journal of Magnetics
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• 제19권2호
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• pp.111-115
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• 2014

X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM) were used to investigate the influence of Ni ions on the structural, electronic, and magnetic properties of nickel-ferrites ($Ni_xFe_{3-x}O_4$). Spinel $Ni_xFe_{3-x}O_4$ ($x{\leq}0.96$) samples were prepared as polycrystalline thin films on $Al_2O_3$ (0001) substrates, using a sol-gel method. XRD patterns of the nickel-ferrites indicate that as the Ni composition increases (x > 0.3), a structural phase transition takes place from cubic to tetragonal lattice. The XPS results imply that the Ni ions in $Ni_xFe_{3-x}O_4$ substitute for the octahedral sites of the spinel lattice, mostly with the ionic valence of +2. The minority-spin d-electrons of the $Ni^{2+}$ ions are mainly distributed below the Fermi level ($E_F$), at around 3 eV; while those of the $Fe^{2+}$ ions are distributed closer to $E_F$ (~1 eV below $E_F$). The magnetic hysteresis curves of the $Ni_xFe_{3-x}O_4$ films measured by VSM show that as x increases, the saturation magnetization ($M_s$) linearly decreases. The decreasing trend is primarily attributable to the decrease in net spin magnetic moment, by the $Ni^{2+}$ ($2{\mu}_B$) substitution for octahedral $Fe^{2+}$ ($4{\mu}_B$) site.

• 대한전자공학회논문지TE
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• 제39권4호
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• pp.341-349
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• 2002

금속산화물 Al₂O₃, CoO, Fe₂O₃ 및 MnO₂를 이트리아 안정화 지르코니아(YSZ)에 첨가하여 전기적, 기계적 그리고 소결성에 미치는 영향을 연구하였다. 정방정에서 단사정으로의 상전이비가 각 첨가물을 8wt% 까지 첨가함에 따라 변화됨을 볼 수 있었고, 소결 밀도는 첨가물량이 증가함에 따라 감소하였다. 파괴인성은 상전이비가 약 18%에서 최대가 되었다. YSZ의 전기전도도는 CoO, Fe₂O₃, 및 MnO₂의 첨가량이 1.5wt%까지 첨가될 때 증가하였다. 그러나 Al₂O₃의 첨가는 YSZ의 전기전도도에 영향이 없었다. 복합첨가의 경우 파괴인성 및 경도에 다소 복잡한 경향을 보였는데, 복합조성 1.5wt%-Fe₂O₃, 3.0wt%-Al₂O₃, 그리고 1.5wt%-CoO 에서 상전이비가 18%, 파괴인성 10.8 MPa·m/sup 1/2/이라는 최고의 값과 경도 1201 kgf/mm² 값을 얻을 수 가 있었다.

• 한국세라믹학회지
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• 제32권6호
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• pp.748-760
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• 1995

Pyroelectric properties, figure of merits, and the other properties of the Pb(Zn1/3Nb2/3)O3-Pb(Fe1/2Nb1/2)O3 system, as expected to have excellent pyroelectric properties in the operating temperature range of pyroelectric type infrared sensor, were investigated. In the Pb(Zn1/3Nb2/3)O3-Pb(Fe1/2Nb1/2)O3 system, suppression of the pyrochlore phase depended on sintering condition, as like sintering temperature, holding time, sintering atmosphere. The specimen, sintered by the same composition atmosphere powder at 105$0^{\circ}C$ for 1.5h, possessed the best physical property. It was found that the piezoelectric parameters were mainly depended on the amount of spontaneous polarization and then the 0.2PZN-0.8PFN showed the best pyro- and piezoelectric properties. In terms of the experimental method, two pyroelectric-testing methods, i.e. static and dynamic methods, had a same tendency. Also the result of pyroelectric testing by the static method indicated that the diffuse phase transitiion resulted in the temperature difference of phase transition between dielectric constant and pyroelectric coefficient.