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Your search keyword '"Sung, Y. S."' showing total 128 results
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128 results on '"Sung, Y. S."'

1. Structural evolution of bismuth sodium titanate induced by A-site non-stoichiometry: Neutron powder diffraction studies

Author

Jeong, I. -K., Sung, Y. S., Song, T. K., Kim, M. -H., and Llobet, A.

Subjects
Condensed Matter - Materials Science
Abstract

We performed neutron powder diffraction measurements on (Bi$_{0.5}$Na$_{0.5+x}$)TiO$_3$ and (Bi$_{0.5+y}$Na$_{0.5}$)TiO$_3$ to study structural evolution induced by the non-stoichiometry. Despite the non-stoichiometry, the local structure ($r$$\leq$ 3.5 {\AA}) from the pair distribution function analysis is barely affected by the sodium deficit of up to -5 mol%. With increasing pair distance, however, the atomic pair correlations weaken due to the disorder caused by the sodium deficiency. Although the sodium and the bismuth share the same crystallographic site, their non-stoichiometry have rather opposite effects as revealed from a distinctive distortion of the Bragg peaks. In addition, Rietveld refinement demonstrates that the octahedral tilting is continually suppressed by the sodium deficit of up to -5 mol%. This is contrary to the effect of the bismuth deficiency, which enhances the octahedral tilting., Comment: 5 pages, 4 figures

Published
2015
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7. Deriving thermophysical properties of liquid Nb by containerless electrostatic levitation.

Author

Sung, Y. S., Takeya, H., and Togano, K.

Subjects
*THERMODYNAMICS, *ELECTROSTATICS, *PHYSICS
Abstract

Containerless solidification of Nb was carried out by the electrostatic levitation process in which a bulk sample was electrostatically levitated and melted by laser irradiation in high vacuum. A t(T) function in a time-temperature profile was analytically determined to describe the radiative cooling curves of Nb in the liquid state to estimate the ratio of constant pressure specific heat to hemispherical total emissivity, c[sub P](T)/ε[sub T](T), and further to derive ε[sub T](T) and c[sub P](T). The cooling behavior of liquid Nb was found to be well described by an inverse biquadratic polynomial of t(T). With the analytical t(T) function, the derivative dt/dT was easily obtained and the c[sub P](T)/ε[sub T](T) ratio was readily estimated from the radiative cooling curve. The estimated c[sub P](T)/ε[sub T](T) and the derived ε[sub T](T) and c[sub P](T) agreed well with the reference data in the literature. This implies the rationale behind the analytical approach taken in this study was reasonable and can be applied to estimating c[sub P](T)/ε[sub T]( T) and further deriving c[sub P](T) or ε[sub T](T) of materials in the liquid state. [ABSTRACT FROM AUTHOR]

Published
2002
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8. Ferroelectric and leakage current behaviors of BiFe[O.sub.3]-Bi ([Zn.sub.1/2][Ti.sub.1/2])[O.sub.3] ceramics

Author

Cho, J.H., Song, T.K., Wang, L., Yeo, H.-G., Sung, Y.-S., Kim, M.-H., and Park, D.-S.

Subjects
Bismuth -- Electric properties, Ferroelectric crystals -- Structure, Iron alloys -- Structure, Iron alloys -- Electric properties, Semiconductor doping -- Analysis, Titanium -- Electric properties, Zinc -- Electric properties, Physics
Abstract

BiFe[O.sub.3]-Bi([Zn.sub.1/2][Ti.sub.1/2])[O.sub.3] (BF-BZT) ceramics are made by a solid state reaction method and crystal structure and microstructure are observed. Two distinctive relaxations are observed and ferroelectric hysteresis loops are observed in BF with low electric field and BZT doped ceramics.

Published
2009

9. Ferroelectric and leakage current behaviors of BiFeO3-Bi(Zn1/2Ti1/2)O3 ceramics.

Author

Cho, J. H., Song, T. K., Wang, L., Yeo, H.-G., Sung, Y.-S., Kim, M.-H., and Park, D.-S.

Subjects
FERROELECTRICITY, CERAMICS, MICROSTRUCTURE, ELECTRIC fields, HYSTERESIS loop, CRYSTALS, SEMICONDUCTOR doping
Abstract

BiFeO3-Bi(Zn1/2Ti1/2)O3 (BF-BZT) ceramics were made by a solid state reaction method. Crystal structure and microstructure were observed. Leakage currents were much reduced with BZT doping in BF. Dielectric constants of BF-BZT increased as frequency is decreased. Two distinctive relaxations were observed at about 500 kHz and 3 Hz. Ferroelectriclike hysteresis loops were observed in BF with low electric field and 2.5 and 5 mol % BZT doped ceramics. [ABSTRACT FROM AUTHOR]

Published
2009
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49. Roles of Li and Ta in Pb-free piezoelectric (Na,K)NbO3 ceramics.

Author

Sung, Y. S.

Subjects
*PIEZOELECTRIC ceramics, *LITHIUM, *PHASE transitions, *TANTALUM, *X-ray diffraction
Abstract

Piezoelectric coefficient (d33) of (Na,K)NbO3 (NKN) is enhanced not only at its morphotropic phase boundary (MPB) composition but also enhanced at its polymorphic phase transition (PPT) temperature between orthorhombic and tetragonal phases (TO-T ). Thus, for NKN-based ceramics, even higher d33 could be obtained if both MPB and PPT are simultaneously optimized. This temperature as well as composition dependence of piezoelectric properties of NKN-based ceramics requires a systematic approach that differentiates factors for MPB and PPT. In this paper, the roles of Li and Ta known to affect d33 and TO-T were identified in relation with lattice parameters. [ABSTRACT FROM AUTHOR]

Published
2014
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