• Progress in Superconductivity
• /
• v.12 no.2
• /
• pp.75-81
• /
• 2011

We report on the progress that has been made in developing $MgB_2$ superconducting wires and tapes for commercialization and research efforts. A number of techniques have been developed to overcome the obstacle posed by the poor critical current density ($J_c$) of pristine $MgB_2$. Chemical doping has proved to be the effective way to modify and enhance the superconducting properties, such as the $J_c$ and the irreversibility field ($B_{irr}$). More than 100 different types of dopants have been investigated over the past 8 years. Among these, the most effective dopants have been identified to be SiC and malic acid ($C_4H_6O_5$). The best results, viz. a $B_{irr}$ of 22 T and $J_c$ of $30,000\;A{\cdot}cm^{-2}$ at 4.2 K and 10 T, were reported for malic acid doped $MgB_2$ wires, which matched the benchmark performance of commercial low temperature superconductor wires. In this work, we discuss the progress made in $MgB_2$ conductors over the past few years at the University of Wollongong, Hyper Tech Research, Inc., and Ohio State University.

• Applied Science and Convergence Technology
• /
• v.25 no.5
• /
• pp.88-91
• /
• 2016

The $Pb[(Mg_{1/3}Ta_{2/3})_{0.7}Ti_{0.3}]O_3$+xwt%PbO systems at temperature of $1250^{\circ}C$ for 4 hours was successful synthesized. In this study, PbO-doped $Pb[(Mg_{1/3}Ta_{2/3})_{0.7}Ti_{0.3}]O_3$ systems with non-linear behaviors showed ordering-degree dependence at the low temperature range were prepared using the columbite precursor method. And the characteristic of remnant polarization vs. electric field were analyzed. The pyroelectric, dielectric and piezoelectric properties of partially disordered $Pb[(Mg_{1/3}Ta_{2/3})_{0.7}Ti_{0.3}]O_3$+xwt%PbO solid solutions were studied as a function of temperature, frequency, and electric field. It showed distinct features of temperature dependent of pyroelectric coefficient, spontaneous polarization and dielectric constant at about $50^{\circ}C$. The figure of merit was calculated as pyroelectric coefficient, dielectric constant and dissipation factor. It was found that the high voltage responsivity FV, high detectivity FD were $0.0373m^2/C$ and $0.6735{\times}10^{-4}Pa{-1/2}$, respectively, in the $Pb[(Mg_{1/3}Ta_{2/3})_{0.7}Ti_{0.3}]O_3$+3.0 wt%PbO system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.6
• /
• pp.356-360
• /
• 2017

We investigated the phase evolution, microstructure, and microwave dielectric properties of Na- and Zr-doped $Ba(Mg_{0.5}W_{0.5})O_3$ [i.e., ($Ba_{1-2x}Na_{2x})(Mg_{0.5-x}Zr_xW_{0.5})O_3$] ceramics. $BaWO_4$ as a secondary phase was observed in all compositions, and it increased as the dopant concentration increased. All specimens revealed a dense microstructure. For the composition of x=0.01, polyhedral grains were observed. As the dopant concentration increased, the densification and the grain growth were promoted by a liquid phase. The quality factor($Q{\times}f_0$) decreased remarkably, whereas the dielectric constant (${\varepsilon}_r$) tended to decrease as the dopant concentration increased. The dielectric constant, quality factor, and temperature coefficient of the resonant frequency of the composition of x=0.01 sintered at $1,700^{\circ}C$ for 1 h were 18.6, 216,275 GHz, and $-22.0ppm/^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.14 no.3
• /
• pp.190-196
• /
• 2001

The microwave dielectric properties and a sintering behavior of MgTiO$_3$-CaTiO$_3$ ceramics doped with Li were investigated. The main composition was fixed as 0.94MMgTiO$_3$-0.06CaTiO$_3$ and Li$_2$CO$_3$was added excessively in the range of 0~10 mol% (with reference to Li atoms) and the specimens were sintered at 1200~140$0^{\circ}C$ for 4 hours. When the amount of Li was small the quality factor and dielectric constant were reduced, while those tow properties increased if the Li amount was above 1 mol%. But if Li was overly added those dielectric properties decreased again. Li, if added in the composition range of 1.0~3.0 mol%, can increase the quality factor of MgTiO$_3$-CaTiO$_3$ ceramics. The optimum amount of Li was 1.5mol% and sinterign condition was 1275$^{\circ}C$/4hr, at which we cudl obtain following results ; dielectric constant ($\varepsilon$$_{r}$) of f20.0, quality factor(Qxf$_{0}$) of 78,000 GHz and temperature coefficient of resonant frequency($\tau$$_{f}$) of -1.6 ppm/$^{\circ}C$.>.>.>.

• Applied Microscopy
• /
• v.27 no.1
• /
• pp.101-109
• /
• 1997

The nonstoichiometric ordering of Mg and Nb cations in undoped and La-doped lead magnesium niobate solid solutions has been investigated by means of high-resolution transmission electron microscopy and computer image simulation. High-resolution lattice images were obtained under various microscope imaging conditions and objective apertures. Computer image simulations were performed for a wide range of sample thickness, defocusing value, and long-range order parameter. The simulated images revealed that the lattice images of the ordered regions were predominantly dependent on the long-range order parameter. From the comparisons of the experimental and simulated images for the ordered regions, the long-range order parameter approximately ranged 0.2 to 0 7. It was also found that the ordered structure has a $(NH_4)_3-FeF_6$ structure, which consists of alternating Mg- and Nb-preferred sublattices along the (111) directions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.4
• /
• pp.212-215
• /
• 2018

The phase evolution, microstructure, and microwave dielectric properties of $Ba(Mg_{0.5-2x}Y_{2x}W_{0.5-x}Ti_x)O_3$ (x = 0.005~0.05) ceramics sintered at $1,700^{\circ}C$ for 1h were investigated. All compositions exhibited a 1:1 ordered cubic perovskite structure. The field emission scanning electron microscopy image revealed a dense microstructure in all the compositions. As the value of x increased, the lattice parameter, dielectric constant, and quality factor increased. The temperature coefficient of resonant frequency changed from $-19.6ppm/^{\circ}C$ to $-5.9ppm/^{\circ}C$ with increasing x value. The dielectric constant, quality factor, and temperature coefficient of resonant frequency of $Ba(Mg_{0.40}Y_{0.10}W_{0.45}Ti_{0.05})O_3$ were 21.7, 132,685 GHz, and $-5.9ppm/^{\circ}C$, respectively.

• Journal of Korean Ophthalmic Optics Society
• /
• v.11 no.3
• /
• pp.165-172
• /
• 2006

On the MgO single crystals doped artificially with Cr, Cu, Fe we observed thermally stimulated luminescence(TSL) glow curves and spectra, and analyzed them in the temperatures range from at liquid nitrogen temperature(77K) to about 500K after excitation with UV or X-ray irradiation. TSL glow curves obtained from these samples show five peaks at 136.5K, 223.5K, 360K, 390K, 440K, and their estimated activation energies are 0.27eV, 0.63eV, 1.08eV, 1.08eV, 1.19eV, and 1.33eV, respectively. When we measured TSL spectrum at the range of 200nm to 650nm on the MgO single crystals. we also analyzed the peak wavelength which obtained at 345nm, 375nm, and 410nm from measurement of TSL spectrum and described their luminescence mechanisms. TSL spectrum peaks emitted from MgO:Cr, MgO:Cu, and MgO:Fe appear at the wavelengths of 345nm, 360nm, and 375nm, respectively.

• Korean Journal of Materials Research
• /
• v.8 no.12
• /
• pp.1170-1175
• /
• 1998

PZT films without lower electrode were deposited on the highly doped Si(100) substrate with MgO buffer layer (Mgo/si) by RF magnetron sputtering method followed by the rapid thermal annealing at $650^{\circ}C$ . We investigated the dependences of the crystalline and electrical properties on the MgO thickness and the RTA post annealing. The PZT films on bare Si (without MgO) showed pyrochlore crystal structure while those on MgO(50 )/Si substrates showed the typical perovskite crystal structures. From SEM and AES analysis, the thickness of PZT films was about 7000 showing relatively smooth interface. The depth profiles indicated that atomic species were distributed homogeneously in the PZT/MgO/Si substrate. The dielectric constant($\varepsilon_{r}$ ) and remanent polarization(2Pr) were about 300 and $14\mu$C/$\textrm{cm}^2$;, respectively. The leakage current was about $3.2\mu$/A$\textrm{cm}^2$.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.48 no.7
• /
• pp.10-16
• /
• 2011

We report on the simulation results of electrical/optical characteristics for nonpolar GaN LED having Mg-doped GaN spacer and quantum barrier, in comparison with those of the typical nonpolar GaN LED. In order to reduce the band-gap energy distortion and conduction-band discontinuity in InGaN/GaN multiple quantum wells(MQWs) of nonpolar GaN LED, and thereby to increase their current-voltage, light output power and emission peak intensity, we applied 6 nm-thick p-type($1{\times}10^{18}\;cm^{-3}$) GaN spacer and GaN QB schemes to the typical nonpolar GaN LED epitaxial structure. As a result, we found that the radiative recombination rate was increased by 23% in MQWs at 20 mA current injection. Also, the forward voltage($V_f$) and the light output power($P_{out}$) were improved by 3.7% and 7%, respectively, for the proposed nonpolar LED epitaxial structure, compared with those of the typical nonpolar GaN LED.

• Journal of the Korean Chemical Society
• /
• v.31 no.3
• /
• pp.215-224
• /
• 1987

The electrical conductuctivity measurements have been made on polycrystalline samples of various compositions in the $MgO-TiO_2$ system from 600 to $1100^{\circ}C$ under $Po_2$'s of $10^{-8}\;to\;10^{-1}$atm. Plots of log ${\sigma}$ vs. 1/T at constant $Po_2$ are found to be linear with the inflections, and the activation energies are 1.94eV for the intrinsic range and 0.48eV for the extrinsic range, respectively. The log ${\sigma}$ vs. log $Po_2$ curves are found to be linear at constant temperature, and the conductivity dependences of $Po_2$ are closely approximated by ${\sigma}\;{\alpha}\;Po_2^{-1/6}$ for the extrinsic and ${\sigma}\;{\alpha}\;Po_2^{-1/4}$ for the intrinsic range, respectively. The dominant defects in this system are believed to be oxygen vacancy for the extrinsic and $Ti^{3-}$ interstitial for the intrinsic range. The conduction mechanisms in both the extrinsic and the intrinsic ranges are proposed by the results of the electrical conductivity dependence on the oxygen partial pressure. Polaron model was suggested in the extrinsic region by the conductivity dependences of temperature and $Po_2$.