• Journal of Magnetics
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• v.18 no.3
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• pp.245-249
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• 2013

A finite element model was built for MnBi/${\alpha}$-Fe nanocomposite permanent magnets, and the demagnetization curves of the magnets were simulated by micro-magnetic calculation. The microstructure of the cubic model is composed of 64 irregular grains with an average grain size of 20 nm. With the volume fraction of soft magnetic phase (t vol. %) ranged from 5 to 20 vol. %, both isotropic and anisotropic nanocomposite magnets show typical single-phase permanent magnets behavior in their demagnetization curves, illustrating good intergranular exchange coupling effect between soft and hard magnetic phases. With the increase of volume fraction of soft magnetic phase in both isotropic and anisotropic magnets, the coercive force of the magnets decreases monotonically, while the remanence rises at first to a peak value, then decreases. The optimal values of maximum energy products of isotropic and anisotropic magnets are 84 and $200kJ/m^3$, respectively. Our simulation shows that the MnBi/${\alpha}$-Fe nanocomposite permanent magnets own excellent magnetic properties and therefore good potential for practical applications.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.268-279
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• 1994

The x-ray powtler pattern of single phase $Bi_2S_2CaCu_2O_{8+x}$ has been identified and fullyindexed using a pseudotetragonal subcell with a= 5.408, c = 30.83 $\AA$ and an incommensurate supercellwith reciprocal lattice vector, X$q^*$, given by $q^*=0.211b^*-c^*$. The x -ray powder pattern of the Pb-free110K superconductor phase "$Bi_2S_2CaCu_2O_{10+x}$" has many lines which belong t.o an incommensuratesupercell. Using elect.ron d~ffraction pImt.ographs as a indexing guide, an indexing scheme for the powderpattern has been obtained. The unit cell has a geometrically orthorhombic subcell a=5.411, b= 5.420, c=37.29(2) $\AA$. Supercell reflections have indices that are derived from the subcell k, 1 indices by addition uf$\pm q^*$, where $\pm q^*=0.211b^*-0.78c^*$The incommensurate con~ponent In the b dwection, $\delta$, is the same for both phases but on going from2212 to 2223 phase, the superlattic component in the c direction changes from commensurate($\varepsilon$=1) toincommensurate($\varepsilon$=0.78).X>$\varepsilon$=0.78).

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.31-34
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• 2003

Bi-2223 superconducting wires with 55 filaments were fabricated by stacking, drawing process with different heat-treatment histories. Two kinds of powders were prepared. One was pre-annealed at 760-820 $^{\circ}C$ and low oxygen partial pressure, and the other was only calcined state. Before rolling process, round wires were pre-annealed at 760 -820 $^{\circ}C$ and in a low oxygen partial pressure. We confirmed that pre-annealing step was to transform Bi-2212 orthorhombic structure from Bi-2212 tetragonal structure and to reduce the formation of second phases at superconducting wire. However Bi-2223 phases were formed at higher pre-annealing temperature. Bi-2223 conductor was needed frequently annealing at low temperature because pre-annealing at precursor powder brought about decrease in workability. We could achieve highest Je of 6500 A/$\textrm{cm}^2$ at the tape using Bi-2212 orthorhombic phase by introduced slightly overheating at the 1st sintering process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.693-696
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• 2001

The (Ba$_{0.3}$Bi$_{0.3}$Sr$_{0.4}$)TiO$_3$[BBST] ceramics were prepared by conventional mixed oxide method. The structural properties of the BBST ceramics with sintering temperature were investigated by XRD, SEM, EDS. In the case of BBST ceramics sintered at 1150~135$0^{\circ}C$, the $Ba_{0.5}$Sr$_{0.5}$TiO$_3$and SrBi$_4$Ti$_4$O$_{15}$ phase were coexisted. The 2$\theta$ value of the BST (110) peaks were shifted to the lower degree at the sintering temperature of 130$0^{\circ}C$ and 135$0^{\circ}C$. The grains of the BBST ceramics sintered at 130$0^{\circ}C$ and 135$0^{\circ}C$ were not appeared. Increasing the sintering temperature, the densities of the BBST ceramics were increased. In the BBST ceramics sintered at 130$0^{\circ}C$ and 135$0^{\circ}C$, the mole ratio of Bi was decreased.d.ed.d.d.d.

• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.87-93
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• 1986

Yttria-bismuth-stabilized zirconia was investigated with respect to the amount of $Bi_2O_3$ addition in the ran-ge of 0.5~5mol% to the base composition of $(ZrO_2)_{0.92}(Y_2O_3)_{0.08}.Bismuth was introduced into the ma-terial with $Bi_2O_3-SiO_2$ glasses in order to reduce the evaporation of components. The sinterbility evaporation of components phase formation and microstructure were evaluated depending on the amount of $Bi_2O_3-SiO_2$ glass addition. Two probe A. C conductivity measurement was subjected to all the specimens and the result was discussed on the possible substitution of $Bi^{3+}$ for $Zr^{4+}$ and interistial $Si^{4+}$ in the fluorite structure of zirconia crystal there-upon the possible change in the capability of oxygen transference within the material. It was found that the addition of $Bi_2O_3$ could improve the sinterbility of material very much while not so much.oxygen sensing material suitable for relative low temperature firing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.236-237
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• 2005

The structural properties of $(Bi,Ce)_4Ti_3O_{12}(BCT)$ thin films with post-annealing temperature were investigated. $(Bi,Ce)_4Ti_3O_{12}(BCT)$ thin films were deposited by RF sputtering method on Pt/Ti/$SiO_2$/Si substrates with optimum deposition condition. The $(Bi,Ce)_4Ti_3O_{12}(BCT)$ thin films was post-annealed at 600$^{\circ}C$, 650$^{\circ}C$, 700$^{\circ}C$, 750$^{\circ}C$, 800$^{\circ}C$ in furnace,respectively. Increasing the post-annealing temperature, the grain size, density and peak intensity of (117) and c-axis orientation were increased. The $(Bi,Ce)_4Ti_3O_{12}(BCT)$ thin films that annealed at 750$^{\circ}C$ exhibited well crystallized phase and had no vacancy and grain was uniform. but there are some secondary phases observed. At this time, the average thickness of $(Bi,Ce)_4Ti_3O_{12}(BCT)$ thin films was 2000 ${\AA}$.

• Journal of Powder Materials
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• v.17 no.4
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• pp.336-341
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• 2010

The present study focused on the synthesis of Bi-Sb-Te-based thermoelectric powder by an oxidereduction process. The phase structure, particle size of the synthesized powders were analyzed using XRD and SEM. The synthesized powder was sintered by the spark plasma sintering method. The thermoelectric property of the sintered body was evaluated by measuring the Seebeck coefficient and specific electric resistivity. The $Bi_{0.5}Sb_{1.5}Te_3$ powder had been synthesized by a combination of mechanical milling, calcination and reduction processes using mixture of $Bi_2O_3$, $Sb_2O_3$ and $TeO_2$ powders. The sintered body of the $Bi_{0.5}Sb_{1.5}Te_3$ powder synthesized by an oxide-reduction process showed p-type thermoelectric characteristics, even though it had lower thermoelectric properties than the sintered body of the $Bi_{0.5}Sb_{1.5}Te_3$ thermoelectric powder synthesized by the conventional melting-crushing method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.91-92
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• 2006

The important merit of Bi-2212/Ag wire is to apply cable as round wire state. Bi-2212 high Tc superconducting wires were fabricated in order to apply Rutherford cable near the future. Various Ag ratio from 0.22 to 0.42 of Ag tubes for PID (powder-In-Tube) process were used to investigate the workability and to prevent breakage of filaments during drawing. In order to find proper heat treatment condition, we investigated micro-structure of Bi-2212/Ag wires by using differential thermal analysis, XRD and SEM. The effect of atmosphere on the peritectic decomposition temperature of precursor was investigated. The shape of grain was observed by SEM to investigate Bi-2212 phase formation in filaments. The higher of Ag ratio of mono filament had the higher critical current density, Jc. The wire with 0.42 of Ag ratio showed 7,886 A/cm2 of Jc at 77K.

• Current Optics and Photonics
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• v.2 no.2
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• pp.147-152
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• 2018

We propose a novel bi-focal metallic Fresnel zone plate (MFZP) with shallow depth-of-field (DOF) characteristics. We design the specific annular slit patterns, exploiting the phase-selection-rule method along with the particle swarm optimization algorithm, which we have recently proposed. We numerically investigate the novel characteristics of the bi-focal MFZP in comparison with those of another bi-focal MFZP having equivalent functionality but designed by the conventional multi-zone method. We verify that whilst both bi-focal MFZPs can produce dual focal spots at $15{\mu}m$ and $25{\mu}m$ away from the MFZP plane, the former exhibits characteristics superior to those of the latter from the viewpoint of axial resolution, including the axial side lobe suppression and axial DOF shallowness. We expect the proposed bi-focal MFZP can readily be fabricated with electron-beam evaporation and focused-ion-beam processes and further be exploited for various applications, such as laser micro-machining, optical trapping, biochemical sensing, confocal sensing, etc.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.388-393
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• 2018

Sublimation of $Bi_2O_3$-based materials is an important degradation issue for the long-term applications of many electronic devices. A series of $SnO_2$-doped $Bi_2O_3$ materials (SBO), was synthesized, densified, and then tested in air or strong reducing atmosphere. The $SnO_2$-doping effects and sublimation kinetics of the SBO materials were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and precise mass loss measurement. The results show that formation of $Bi_2Sn_2O_7$ phase greatly retards the mass loss of SBO. The SBO samples show a surface sublimation in an energy of $52.6kJ{\cdot}mol^{-1}$. However, the sublimation is also controlled by surface microstructure as the amount of vaporizing species (the Bi or gaseous Bi-oxides) is more than 0.1 mass%. The evaporation is retarded on the rough surface and the mechanism of surface evaporation is changed to diffusional control.