• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.1-5
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• 2012

$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ hollow fiber with o.d. 1.02 mm and i.d. 0.437 mm were fabricated by a phase-inversion spinning technique.The starting $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ precursor was synthesized by the polymerized complex method and then calcined at $900^{\circ}C$. As-prepared powder was dispersed in a polymer solution, and extruded as form of hollow fiber through a spinneret. Finallydense $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ hollow fiber membrane was obtained by sintering for 2 h at $1,080^{\circ}C$ for the application of oxygen separation. In addition, despite a very thin membrane with 0.58 mm, the BSCF hollow fiber membrane possessed a proper mechanical strength of 602.5 MPa.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.543-553
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• 1996

Oxygen reduction in an alkaline fuel cell was studied by using perovskite type oxides as an oxygen electrode catalyst. The high surface area catalysts were prepared by malic acid method and had a formula of $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$(x=0.00, 0.01, 0.10, 0.20, 0.35 and 0.50). From the result of XRD pattern and specific surface area due to the amount of Fe substitution and the consumption of ammonia-water, the complex formation of Fe ion with $NH_3$ was the main factor for both the phase stability of perovskite and the increase of specific surface area. Multi-step calcination was necessary to give a single phase of perovskite in catalyst precursor. The crystal structure of the catalysts was simple cubic perovskite, which was verified from the XRD patterns of the catalysts. The activity of oxygen reduction was monitored by the techniques of cyclic voltammetry, static voltage-current method, and current interruption method. The activity(current density) of oxygen reduction showed its minimum at x=0.01 and its maximum between 0.20 and 0.35 of x-value in $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$. This tendency was independent of the change of surface area.

• Progress in Superconductivity
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• v.12 no.1
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• pp.46-50
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• 2010

In the superconducting $Sr_2VO_3FeAs$, containing bimetallic layers, with maximum $T_c{\approx}\;46\;K$ correlation effects on V ions have been investigated using LDA+U method. Within the local density approximation (LDA) this system has the one-third filled $t_{2g}$ manifold of V, decomposed into $d_{xy}$ of bandwidth W=2 eV and nearly degenerate $d_{zx}d_{yz}$ of W=1 eV. Consideration of correlation effects leads to a metal-insulator transition on V ions $t^{2\uparrow}_{2g}\;{\rightarrow}\;d^{1\uparrow}_{xz}\;d^{1\uparrow}_{yz}$ at the critical on-site Coulomb repulsion $U_c$= 3.5 eV. At U=4 eV, the electronic structure, in which V ions are insulating, leads to several van Hove singularities near $E_F$ and similar Fermiology with other pnictides. Applying U to V ions results in increasing Fe moment as well as V moment, indicating somewhat hybridization between Fe and V ions even though this system is strongly 2-dimesional. Our results show possible importance of correlation effects on this system.

• Resources Recycling
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• v.11 no.5
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• pp.16-20
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• 2002

This experiment was carried out to examine the effects of La-Co substitution on Sr-ferrite. The magnetic properties of calcined and sintered materials varied with the substitutional amount of La and Co elements in Sr-ferrite. Anisotropy field and coercivity for Sr ferrite were increased with raising La-Co substitution amounts. The microstructure observation for Sr ferrite substituted by La-Co revealed that La-Co inhabited grain growth during calcination and promoted lateral grain growth during sintering. The relationship between $B_{r}$ and $_{i}$ /$H_{c}$ for La-Co substituted Sr-ferrite was found to be $B_{r}$$≒0.097_{i}$ /$H_{c}$/+4500. In case of $SrFe_{12}$ $O_{19}$, $B_{r} was 4090 G and $_{ i}$$H_{c}$ was 3560 Oe, but $B_{r}$ was 4080 G and and $_{i}$ $H_{c}$ was 4800 Oe for $Sr_{0.7}$ $La_{0.3}$ $Fe_{11.7}$ /$Co_{0.3}$ $O_{19}$.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3407-3412
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• 2012

The Ti incorporation at Fe-site in the double perovskite lattice of $Sr_2FeNbO_6$ (SFNO) system is studied. The Ti concentration optimization yielded an efficient photocatalyst. At an optimum composition of Ti as x = 0.07 in $Sr_2Fe_{1-x}Ti_xNbO_6$, the photocatalyst exhibited 2 times the quantum yield for photolysis of $H_2O$ in presence of $CH_3OH$, than its undoped counterpart under visible light (${\lambda}{\geq}420nm$). Heavily Ti-doped $Sr_2Fe_{1-x}Ti_xNbO_6$ lattice exhibited poor photochemical properties due to the existence of constituent impurity phases as observed in the structural characterization, as well as deteriorated optical absorption. The higher electron-density acquired by n-type doping seem to be responsible for the more efficient charge separation in $Sr_2Fe_{1-x}Ti_xNbO_6$ (0.05 < x < 0.4) and thus consequently displays higher photocatalytic activity. The Ti incorporated structure also found to yield stable photocatalyst.

• Journal of the Korean Ceramic Society
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• v.44 no.11
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• pp.627-632
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• 2007

We have studied the ac conductivity of insulating $La_{0.7}Sr_{0.3}FeO_3$ in the frequency range 20 Hz-l MHz and in the temperature range 80-300 K. We have analyzed experimental results in the frame works of the quantum-mechanical tunneling mechanism (QMT) and the hopping of barrier mechanism (HOB). We observed that small polaron QMT model is the most suitable mechanism for the low temperature ac conductivity of $La_{0.7}Sr_{0.3}FeO_3$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.1
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• pp.36-41
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• 2002

Abstract The stoichiometric and double-ordered perovskite $Sr_2FeMoO_6$ (SFMO) polycrystalline ceramics were fabricated by sintering at above $900^{\circ}C$ in $H_2$(5%)/Ar reductive ambient. SMO polycrystals showed good ferromagnetic properties andmagnetrotesistqnce ratios of about 15 % at 8K and 3 % at room temperature. Amorphous SFMO thin films were deposited on $LaA1O_3$ and $SrTiO_3$ single crystal substrates using rf sputtering method with the SFMO polycrystalline ceramic target. Double-ordered perovskite polycrystalline SFMO thin films were fabricated by solid state crystallization by annealing the deposited amorphous films at above $680^{\circ}C$ in $H_2$(5%)/Ar reductive ambient. SFMO thin films exhibited ferromagnetic behavior. Their magnetroresistance ratios, however, were only 0.3~0.5% at 8K and disappeared with increasing the measuring temperature. This was attributed to the absence of magnetic spin tunneling between grains due to the porous structure and non-stoichiometric composition of the deposited films.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.3
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• pp.274-279
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• 2018

Sc-substituted $La_{0.6}Sr_{0.4}FeO_{3-{\delta}}$(LSFSc) has synthesized for ceramic interconnector of tubular solid oxide cells (SOCs). For improving the redox stability and electric conductivity of LSFSc, the compositions of Sc, pH value of mixed precursors, calcination temperature and times were optimizing. The electrochemical performances of $La_{0.6}Sr_{0.4}Fe_{1-x}Sc_xO_{3-{\delta}}$ powders were measured as depending on Sc composition. The electric conductivity and redox stability of $La_{0.6}Sr_{0.4}Fe_{1-x}Sc_xO_{3-{\delta}}$ was determined by Sc concentration. $La_{0.6}Sr_{0.4}Fe_{0.9}Sc_{0.1}O_{3-{\delta}}$ powders can be one of the stable composition for ceramic interconnector of tubular-SOCs.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.156-157
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.88-89
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• 2002