• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.1
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• pp.72-78
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• 1998

Polarization mode converters have been produced by utilizing Ti:LiNbO$_{3}$ channel waveguide and strain-optic effect. Shear strain for periodic perturbations of optical channel waveguides and phase matching can be obtained by an evaporated periodic SiO$_{2}$ thin film at 300.deg. C. The electrodes located on the either side of waveguide provide a means to electro-optically tune the wavelength for maximum polarization conversion via the electrooptic effect. The maximum conversion effeciency was observed at 21.deg. C for V=0 and 46.deg. C for V=30V aro the device having 7 .mu.m waveguide wiith and 350 periodic pads. The dependence of the number of pads on conversion efficiency was observed experimentally.fficiency was observed experimentally.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.237-239
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• 1993

$MnO_2$ added $(Pb_{0.45}Ca_{0.55})(Fe_{0.5}Nb_{0.5})O_3$ was calcined at $850^{\circ}C$ for two hours and sintered at $1100^{\circ}C$ for two hours. The microstructure was examined using XRD and SEM. The dielectric constant, the quality factor, and the temperature stability was measured using Hakki and Coleman method. Dielectric constant was improved to 94 from 0.5wt% $MnO_2$ added sample with $Q{\cdot}f=4260GHz$ and acceptable ${\tau}_f$ (< $20ppm/^{\circ}C$).

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1041-1043
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• 1999

In this work, a possible new PD detection technique, based on the electro-optic effect, has been proposed. A proto-type probe sensor for detection partial discharge is made by $LiNbO_3$ Pockels cell, diachroic sheet polarizer and right-angle prism. The Mach-Zehnder interferometer system is proposed by using this sensor and this system is applied to detecting high electric field. we show the characteristic of the proto-type probe sensor and the design of a proposed probe type sensor.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1232-1233
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• 2006

To co-fire with commercial LTCC (Low Temperature Co-fired Ceramic) materials at $850^{\circ}C{\sim}880^{\circ}C$, different contents of $B_2O_3$ were added to the $Bi_2O_3-ZnO-Nb_2O_5$ (BZN) ceramics. According to the test results, the cubic phase of BZN was transformed into orthorhombic in all the test materials. $BiNbO_4$ phase was formed in test materials with $2{\sim}5wt%$ of $B_2O_3$ addition. The phase transformation of cubic BZN was controlled during the synthesis process with excess ZnO content. The Cubic and orthorhombic phases of BZN could coexist and be sintered densely at $850^{\circ}C/2hr$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.12 no.1
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• pp.62-68
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• 1999

Ferroelectric $Sr_{0.7}/B_{2.3}(Ta_{1-x}Nb_x)_2O_9$(x=0, 0.1, 0.2, 0.3) thin films were deposited on $Pt/SiO_2/Si$ substrate by MOD(Metalorganic Decomposition) process. Metal carboxylate and metal alkoxide were used as precursors, and 2-methoxyethanol, xylene as solvents. After spin coating, thin films were pre-annealed at $400^{\circ}C$, followed by RTA(Rapid Thermal Annealing) and final annealing at $800^{\circ}C$ in oxygen atmosphere. These procedures were repeated three times to obtain thin films with the thickness of $2000{\AA}$. To enhance the nucleation and growth of layered-perovskite phase, thin films were rapid-thermally annealed above $720^{\circ}C$ in oxygen atmosphere. As RTA temperature increased, fluorite phase was transformed to layered-perovskite phase. And the change of Nb contents affected dielectric / electrical properties and microstructure. The ferroelectric characteristics of $Sr_{0.7}/B_{2.3}(Ta_{1-x}Nb_x)_2O_9$ thin film were Pr=8.67 $\mu{C}/cm^2$, Ec=62.4kV/cm and $I_{L}=1.4\times10^{-7}A/cm^2$ at the applied voltage of 5V, respectively.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.121-127
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• 2011

The mechanical properties of the various heat treatment conditions on Ti-15Mo-3Nb-3Al-0.2Si alloy plates were examined. XRD patterns from the surface of Ti-15Mo-3Nb-3Al-0.2Si were analyzed as a solution-treated Ti alloy has the single-phase ${\beta}$ structure whereas the aged Ti alloys have the ${\beta}$ matrix embedded with ${\alpha}$ needles. High strength (~1500 MPa) with decent ductility (7%) was obtained by the Ti alloy double aged at $300^{\circ}C$ and $520^{\circ}C$ for 8 hours each. The double-aged alloy exhibits the finer structure than the single-aged alloy at $300^{\circ}C$ for 8 hours because of the higher nucleation rate of ${\alpha}$ needles at an initial low aging temperature ($320^{\circ}C$). TEM observation revealed that the fine nanostructure with ${\alpha}$ needles in the ${\beta}$ matrix ensured the excellent mechanical properties in the double aged Ti-15Mo-3Nb-3Al-0.2Si alloy. In the solution treated alloy, the yield drop, stress-serrations and the ductility minimum typically associated with dynamic strain aging can be attributed to the dynamic interaction between dislocations and oxygen atoms. The yield drop and the stress serration were not observed in aged samples because the geometrically introduced dislocations due to phase precipitates suppressed the dynamic strain aging.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.925-929
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• 2009

In this study, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3$ ceramics were investigated as a function of the amount of $Ag_2O$ addition in order to improve dielectric and piezoelectric properties of lead-free piezoelectric ceramics. With increasing the amount of $Ag_2O$ addition, density and electromechanical coupling factor ($k_p$) increased up to 0.2 wt.% $Ag_2O$ and decreased above 0.2 wt.% $Ag_2O$. At the sintering temperature of $1020^{\circ}C$, electromechanical coupling factor ($k_p$), density, dielectric constant (${\varepsilon}r$) and curie temperature (Tc) of ceramics with 0.2 wt% $Ag_2O$ showed the optimal values of 0.42, $4.33\;g/cm^3$, 738 and $393^{\circ}C$, respectively.

• Nuclear Engineering and Technology
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• v.35 no.6
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• pp.529-536
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• 2003

The objective of this study is to investigate the reorientation of hydrides with applied stress intensity factor, the peak temperature and the time when to apply the stress intensity factor in a Zr-2.5Nb pressure tube during its thermal cycle treatment. Cantilever beam (CB) specimens with a notch of 0.5 mm in depth made from the Zr-2.5Nb tube were subjected to electrolytic hydrogen charging to contain 60 ppm H and then to a thermal cycle involving heating to the peak temperature of either 310 or $380^{\circ}C$, holding there for 50 h and then cooling to the test temperature of $250^{\circ}C$. The stress intensity factor of either 6.13 or $18.4\;MPa\sqrt{m}$ was applied at the beginning of the thermal cycle, at the end of the hold at the peak temperatures and after cooling to the test temperature, respectively. The reorientation of hydrides in the Zr-2.5Nb tube was enhanced with the increased peak temperature and applied stress intensity factor. Furthermore, when the CB specimens were subjected to $18.4\;MPa\sqrt{m}$ from the beginning of the thermal cycle, the reoriented hydrides occurred almost all over the Zr-2.5Nb tube, surprisingly suppressing the growth of a DHC crack. In contrast, when the CB specimens were subjected to the stress intensity factor at the test temperature, little reorientation of hydrides was observed except the notch region, leading the Zr-2.5Nb to grow a large DHC crack. Based on the correlation between the reorientation of hydrides and the DHC crack growth, a governing factor for DHC is discussed along with the feasibility of the Kim's DHC model.

• Polymer(Korea)
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• v.27 no.5
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• pp.429-435
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• 2003

Vinyl addition copolymerizations of norbornene (NB) and 5-vinyl-2-norbomene (VNB) were carried out using a cationic η$^3$-allyl palladium catalyst in the various mole ratio of comonomers. The copolymers could be obtained in good yield (65∼85%) with high weight-average molecular weights (M$_{w}$ > 760,000). Depending on increasing VNB contents, the molecular weight and yield of the copolymers decreased. FT-IR analysis confirmed that actual contents of VNB in polymer were proportional to the feeding content of VNB. From $^1$H-NMR spectroscopy, we found that both exo and endo VNB isomer were copolymerized with NB. Thermal stabilities of NB-VNB copolymers were independent on the VNB content and their initial decomposition temperatures were about 300 C. The NB-VNB copolymers were followed by epoxidation by using m-CPBA and hydroxylation by 9-BBN, respectively, and these post-polymers were characterized by FT-IR spectroscopy and $^1$H-NMR analysis..

• Journal of the Korean Ceramic Society
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• v.41 no.7
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• pp.508-512
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• 2004

For abutment of dental implants, (Y, Nb)-TZP/Alumina composites were prepared by addition of 10-90 vol% alumina at an interval of 10 vol％ into tetragonal zirconia solid solution which consists of 90.24 mol% Zr $O_2$, 5.31 mol% Y$_2$ $O_3$, and 4.45 mol% Nb$_2$O$\_$5/. Biaxial flexure strength and fracture toughness of composite were optimized by adding 10 vol% alumina, which resulted in 900 MPa and 8.9 MPam$\^$1/2/, respectively. The composite did not undergo low temperature degradation even after autoclave treatment at 200$^{\circ}C$ for 10 h. 65 of (Y, Nb)-TZP/Alumina composite abutments were employed into 40 patients and any adverse reaction, screw loosing, or fracture of abutments was not observed for the span of 2 years, indicating that the ceramic abutments can be safely used for restorations.