• Bulletin of the Korean Chemical Society
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• v.17 no.2
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• pp.168-172
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• 1996

The variations of the structural detail of layered perovskite-type oxides, Na2Ln2Ti3O10 (Ln=La, Nd, Sm, Gd), have been refined by Rietveld analyses of their powder X-ray diffraction data. Although the c-axis strongly decreases from Ln=La to Nd, Sm, or Gd, the length of Na-O bond along the c-axis that is regarded as the sodium layer spacing is not dependent on the unit cell parameter. Such a behavior is explained by the fact that Na-O bond is in competition with Ti-O one of the perovskite slab. Increased covalency of this Ti-O bond by the lattice contraction leads to weakening of the attaching strength of Na ion. This picture is consistent with the experimental observation that Na ion conductivity of Na2Ln2Ti3O10 increases from Ln=La to Nd, Sm, or Gd despite strong contraction of the unit cell volume.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.176-183
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• 2011

The electrochemical characteristics from various particle sizes of $Ce_{0.9}Gd_{0.1}O_{2-{\delta}}$ (CGO91) in composite cathode comprised of the samarium-strontium doped layered perovskite ($SmBa_{0.5}Sr_{0.5}Co_2O_{5+{\delta}}$) and CGO91 have been investigated for possible application as a cathode material for an intermediate temperature-operating solid oxide fuel cell (IT-SOFC). The area specific resistances (ASRs) of composite cathodes with CGO91 having smaller particle size ($0.4\sim42{\mu}m$) and SBSCO of 1 : 1 ratio (50wt% SBSCO and 50 wt% CGO91, SBSCO: 50) give the lowest ASR of $0.10{\mu}cm^2$ at $600^{\circ}C$ and $0.013{\Omega}cm^2$ at $700^{\circ}C$. However, composite cathodes with having relatively bigger CGO91 particle size show the two times higher ASR results than those of SBSCO : 50. From the 10 times thermal cycles in SBSCO : 50, the ASRs of SBSCO : 50 increased from $0.0193{\Omega}cm^2$ to $0.094{\Omega}cm^2$ at $700^{\circ}C$, however, the ASR value was maintained after 7 times of thermal cycling.

• Journal of Magnetics
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• v.5 no.1
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• pp.13-15
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• 2000

We have investigated the finite temperature magnetic ordering in the quasi-two-dimensional Heisenberg antiferromagnetic system $(C_nH{2n+1}NH_3)_2MnCl_4$ with various chain lengths n. Our results far the transition temperatures and the exchange energies for long chain compounds are in marked contrast to previous expectations.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.360-364
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• 2003

$Sr_{l}$ $\pm$x/$Bi_{2}$ $\pm$y/$Ta_2$ $O_{9}$ and $Sr_{l}$ $\pm$$Bi_{x}$ $2\pm$y$Nb_2$$O_{9}$ ceramics were prepared by a solid state reaction method. X-ray diffraction analysis indicated that single-phase of Bi-layered perovskite was obtained. According to Sr/Bi content ratio, Curie temperature( $T_{c}$), electromechanical factor($K_{p}$ ) and mechanical quality factor($Q_{m}$ ) were measured. The Curie temperature of SBN(SBT) rose from $414^{\circ}C$(314$^{\circ}C$) to $494^{\circ}C$(426$^{\circ}C$) when Sr/Bi content ratio was increased. In the case of Sr/Bi content ratio = 0.55/2.3, the maximum value of the mechanical quality factor $Q_{m}$ of SBT and SBN were obtained 3320 and 1010, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.222-227
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• 2020

Pb(Zr,Ti)O₃(denoted as PZT) in the perovskite phase is used as a dielectric, piezoelectric, and super appetizer material owing to its ferroelectric properties. A PZT film was formed by an RF magnetron sputtering process by preparing a target composed of Pb_1.3(Zr_0.52Ti_0.48)O₃. The PZT film was formed by dividing the material into a mono-layer PZT produced continuously with the same sputtering power and a bi-layer PZT produced with two-stage sputtering power. The bi-layer PZT consisted of a lower layer produced under low-power sputtering conditions and an upper layer produced under the same conditions as the mono-layer PZT. XRD revealed small amounts of pyrochlore phase in the mono-layer PZT, but only the perovskite phase was detected in the bi-layer PZT. SEM and AFM revealed the upper part of the bi-layer PZT to be more compact and smooth. Moreover, the bi-layered PZT showed superior symmetry polarization and a significantly reduced leakage current of less than 1×10-5 A/cm². This phenomenon observed in bi-layer PZT was attributed to the induction of growth into a pure perovskite phase by suppressing the formation of a pyrochlore phase in the upper PZT layer where the densely formed lower PZT layer was produced sequentially.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.245-248
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• 2003

Randomly oriented ferroelectric cerium-substituted $Bi_4Ti_3O_{12}$ thin films have been prepared by using metal-organic decomposition method. The layered perovskite structure was investigated using annealing for 1 h in the temperature range from $550\;{\sim}\;750\;^{\circ}C$. The structure and morphology of the films were characterized using X-ray diffraction and scanning electron microscopy The $Bi_{3.4}Ce_{0.6}Ti_3O_{12}$ (BCeT) thin films showed a perovskite phase and dense microstructure. The grain size of the BCeT films increasedwith increasing annealing temperature. The hysteresis loops of the films were well defined at temperatures above $600\;^{\circ}C$. The 200-nm-thick BCeT thin films annealed at $650\;^{\circ}C$ showed a large remanent polarization (2Pr) of 59.3 ${\mu}C/cm^2$ at an applied voltage of 10 V. The BCeT thin films showed good fatigue endurance up to $5\;{\times}\;10^9$ bipolar cycling at 5 V and 100 kHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.217-220
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• 2000

The SrBi$_2$Ta$_2$O$\_$9/(SBT) thin films are deposited on Pt-coated electrode(Pt/TiO$_2$/SiO$_2$/Si) using RF sputtering method. The SBT thin films deposited on substrate at 400-500[$^{\circ}C$]. SBT thin film deposited on Pt-coated electrodes have the cubic perovskite structure and polycrystalline state. With increasing annealing temperature from 600[$^{\circ}C$] to 850[$^{\circ}C$], flourite phase was crystallized to 650[。 and Bi-layered perovskite phase was crystallize ed above 700[$^{\circ}C$]. The maximum remnant polarization and the coercive electric field is 11.73[${\mu}$C/$\textrm{cm}^2$], 85[kV/cm] respectively at annealing temperature of 750[$^{\circ}C$]. The fatigue characteristics of SBT thin films deposited on Pt/TiO$_2$/SiO$_2$/Si substrate did not change up to 10$\^$10/ switching cycles.

• Bulletin of the Korean Chemical Society
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• v.27 no.6
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• pp.853-856
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• 2006

Dion-Jacobson phases $CsCa_2Nb_2FeO_9$ and $CsCa_2Nb_2AlO_9$ were reinvestigated by the Rietveld analysis of powder X-ray diffraction (XRD) method, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). These nominal compounds, previously known as the oxygen-deficient layered perovskites with the sequences of $NbO_6-MO_4-NbO_6$ in tripled slab, in fact, were mixed phases of n = 3 Dion-Jacobson phases and impurities such as $Ca_2NbFeO_6$ and $Ca_3Al_2O_6$. The difference of morphology and chemical in-homogeneity between Dion-Jacobson phases and impurities could be clearly identified by scanning electron microscopy with energy-dispersive X-ray spectroscopy. The chemical composition of $CsCa_2Nb_2FeO_9$ was calculated into $Cs_{0.59}Ca_{2.64}Nb_{2.92}Fe_{0.81}$ in small agglomerate crystals and $Cs_{0.95}Ca_{1.97}Nb_{3.08}Fe_{0.15}$ in long plate-like crystals.

• Journal of the Korean Magnetics Society
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• v.9 no.3
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• pp.131-135
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• 1999

The electronic structures and properties of layered perovskite $LaSrMnO_4$ and $SR^2MnO_4$ have been determined using the local-density full potential Imearized augmented plane wave method. The total energy calculations show that the antiterromagnetic state has lower energy than the ferromagnetic state in $LaSrMnO_4$. The jahn-Teller distortion of Mn-O octahedron produces the energy gap and the $3z^2-r^2$ orbital ordering, which stabilizes 2 dimensional antiferromagnetis state.

• Korean Journal of Materials Research
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• v.13 no.12
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• pp.846-849
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• 2003

Doping effect of various ions in Bi-layered ferroelectric $SrBi_2$$Nb_2$$O_{9}$ (SBN) ceramics was studied. Undoped SBN ceramic and SBN ceramics doped with $Ba^{2＋}$, $Pb^{2＋}$,$ Ca^{2＋}$ , $Bi^{3＋}$ , $La^{3＋}$ , $Ti^{4＋}$ , $Mo^{6＋}$ , and $W^{6＋}$ ions were made by a solid state reaction. Dielectric constants were measured with temperature. Ferroelectric transition temperature decreased with $Pb^{2＋}$ , $Ba^{2＋}$ , $La^{3＋}$ doping, but the transition temperature increased with $Ca^{2＋}$ , $Bi^{3＋}$ , $Ti^{4＋}$, $Mo^{6＋}$ , or$ W^{6＋}$ ionic doping. These results show that the ion size plays an important role in the ferroelectricity of SBN ceramic.