• Korean Journal of Materials Research
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• v.21 no.11
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• pp.628-633
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• 2011

Studies on lead-free piezoelectrics have been attractive as means of meeting environmental requirements. We synthesized lead-free piezoelectric $(Bi_{1/2}Na_{1/2})TiO_3-Ba(Cu_{1/3}Nb_{2/3})O_3$ (BNT-BCN) ceramics, and their dielectric, piezoelectric, and strain behavior were characterized. As BCN with a tetragonal phase was incorporated into the rhombohedral BNT lattice, the lattice constant increased. A small amount of BCN increased the density and dielectric constant forming the complete solid solution with BNT. However, BCN above 10 mol% was precipitated into a separate phase, and which was detected with XRD. In addition, EDX measurement revealed that Cu in BCN was not distributed homogeneously but was accumulated in a certain area. A lower density with a large amount of BCN was attributed to the nonsinterable property of BCN with large tetragonaliy. The dielectric constant vs the temperature change and the strain vs the electric field indicated that the ferroelectric property of BNT was diminished and paraelectric behavior was enhanced with the BCN addition. BNT-7.5BCN showed a 0.11% unimorph strain with a 9.0 kV/mm electric field with little hysteresis.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.1
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• pp.27-34
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• 2001

Refining of powder particles and their dissolution into the Al matrix during mechanical alloying(MA) were investigated by using X-ray diffraction(XRD) transmission electron microscopy (TEM) functions of alloy composition, milling time and ball to powder ratio(BPR). It is found that Ti particles less than 20nm are observed in a dark field image of mechanically alloyed Al-10wt%Ti whose XHD pattern exhibits no Ti peak. The observed change of lattice constant of AI indicates that about 1 wt%Ti can he solved in Al after MA for a long time, independent of alloy composition, milling time and BPR, suggesting that most of Ti particles arc retained in the Al matrix. It is concluded that the disappearance of XRD peaks in mechanically alloyed Al-10wt%Ti is not simply attributable to the dissolution of Ti into Al, but associated mainly with extreme refining and/or heavy straining of Ti Particles.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.414-419
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• 2007

This paper describes the prediction of aerodynamic performance and wake of HAWT in normal and yawed flow operation using potential based methods. In order to analyze aerodynamic performance of wind turbine WINFAS program is used, which is based on VLM(Vortex Lattice Method) and CVC(Constant vorticity contour) Free wake model. Some problems of CVC vortex filament method are investigated arid to improve these problems vortex ring wake are introduced in behalf of CVC vortex filament. The prediction results using the vortex lattice wake are compared to experimental data.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.1
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• pp.56-65
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• 2007

This paper describes physical meanings of various influences of cavity (or pillar) shape and filling factor of dielectric material on band structures in two-dimensional photonic crystals. Influences of circular and rectangular cross-sections of cavity (or pillar) arrays on photonic band structures are considered theoretically, and significant aspects of square and triangular lattices are compared. It is shown that both averaged dielectric constant of the photonic crystal and distribution profile of photon energy play important roles in designing optical properties. For the triangular lattice, especially, it is shown that cavity array with a rectangular cross-section breaks the band structure symmetry. So, we discuss this point from the band structure and address optical properties of lattice with a circular cross-section cavity.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.227-250
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• 1999

The reproducibility of successive growth of Bi12TiO20(BTO) single crystals using a top-seeded solution growth (TSSG) pulling method was evaluated by measuring the lattice constants and their standard deviations. A substantial phase diagram in the region close to the stoichiometric BTO was established experimentally for this purpose, and the existence of a retrograde solid solution close to a BTO was clarified. It was emphasize that a starting solution, with a 10.0~10.1 mol% TiO2 concentration, results in large single crystals with a highly homogeneous lattice constant of within $\pm$1x10-4$\AA$, when the solidified fraction of the grown crystal is less than about 45%. A wavelength dispersion of refractive index was measured for the first time, an it was verified that the refractive index of BTO is larger than that of BSO(Bi12TiO20), allowing the voltage sensitivity of EOS higher than the case with BSO as a probe head.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.424-431
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• 1999

The reproducibility of successive growth of $Bi_{12}TiO_{20}$ (BTO) single crystlas using a top-seeded solution growth (TSSG) pulling method was evalutated by measuring the lattice constants and their standard deviations. A substantial phase diagram in the region close to the stoichiometric BTO was established expermentally for this purpose, and the existence of a retrograde solid solution close to a BTO was clarified. It was emphasized that a starting solution, with a 10.0~10.1 mol% $TiO_{2}$ concentration, results in large single crystals with a highly homogeneous lattice constant of within ${\pm}1{\times}10^{-4}\AA$, when the solidified fraction of the grown crystal is less than about 45 %. A wavelength dispersion of refractive index was measrued for the first time, and it was verified that the refractive index of BTO is larger than that of BSO($Bi_{12}TiO_{20}$), allowing the voltage sensitivity of EOS higher than the case with BSO as a probe head.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.741-746
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• 1990

Dielectrics which do not lose their high insulation resistance in reducing atmosphere are necessary for multilayer ceramic capacitors with Ni internal electrode. In this study we investigated the Ca ion site occupancy in A-site excess Ca-doped BaTiO3 by measuring the insulation resistance, lattice constant and Curie temperature. Its Curie temperature, which was lower than that of the pure BaTiO3, was more lowered by sintering in reducing atmosphere. Lattice constnat of c-axis decreased and that of a-axis increased, suggesting substitution of Ca ions for Ti ions. Hence CaTi" acts as an acceptor to maintain high insulation resistance.ance.

• Journal of Magnetics
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• v.5 no.4
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• pp.143-146
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• 2000

In this study, the magnetic properties of CoCrPt films (far longditudinal recording) on a novel VMn underlayer were measured and compared with similar films on conventional Cr underlayers. It was found that the VMn film had (200) preferred orientation and the lattice constant was about 0.2967 nm, which is slightly larger than that of the Cr film, 0.2888 m. The grain size of the VMn film was 9.8 nm at 30 m thickness, about 39% smaller than that of a similarly deposited Cr. The CoCrPt/VMn films showed higher coercivity in comparison with the CoCrPt/Cr films. The coercivity increase is attributed to the increased Co (11.0) texture, improved lattice matching between Co (11.0) and VMn (200), and lower stacking fault density. V or Mn must have diffused into the CoCrPt magnetic layer uniformly rather than preferentially along grain boundaries. This reduced Ms at higher substrate temperature.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.55-58
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• 2022

Carbon-based doping to MgB₂ superconductor is the simplest approach to enhance the critical current densities under magnetic fields. Carbon quantum dots is synthesized in this work as a carbon provider to MgB₂ superconductors. Polyvinyl Pyrrolidone is pyrolyzed and dispersed in dimethylfomamide solvent as a dopant to the mixture of Mg and B powders. Doped MgB₂ bulk samples clearly show the decrease of a-axis lattice constant, grain refinements, and broadening of FWHM of diffraction peaks compared to un-doped MgB₂ possibly due to the carbon substitution and/or boron vacancy at the boron site in MgB₂ lattice. Also, high-field J_c for the doped MgB₂ is enhanced significantly with the crossover about 3 T at 5 & 20 K when increasing the doping of carbon quantum dots.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.352-362
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• 2000

In this study, effects of novel VMn underlayer on magnetic properties of CoCrPt/VMn longitudinal medium was studied and compared with those of CoCrPt/Cr medium. It was found that the VMn film had (200) preferred orientation and the lattice constant was about 0.2967 nm, which is slightly larger than that of the Cr, 0.2888 nm. The grain size of VMn film was 9.3 nm at 30 nm thickness, and this is about 38 % smaller than that of a similarly deposited Cr film. The CoCrPt/VMn films showed higher coercivity in comparison with the CoCrPt/Cr films. The coercivity increase seems to be attributed to the increased Co (11.0) texture, improved lattice matching between Co (11.0) and VMn (200), and lower stacking fault density. Mn must have diffused into the CoCrPt magnetic layer more uniformly rather than preferentially along grain boundaries this reduced Ms at higher substrate temperature