• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.3
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• pp.95-100
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• 1990

We fabricated primary and secondary seed grains. Primary seed grains having larger grain size were obtained under the conditions that were 2.0mol.% $BaCO_3$ and 10 hours sintering. The amount of primary seed grain that yield the largest secondary seed grain was chosen as 3wt.% and we fabricated the low voltage varistors which were jointed the low voltage-oriented ZnO varistor system made by conventional method with the secondary seed grains. As a result, the ZnO varistors under those conditions showed approximately 10V/mm of nonlinear resistance and 15-22 of nonlinear exponent.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.961-968
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• 2012

In this study, we have investigated the effects of Mn and Co co-doping on defects, J-E curves and grain boundary characteristics of ZnO-$Bi_2O_3$ (ZB) varistor. Admittance spectra and dielectric functions show two bulk defects of $Zn_i^{{\cdot}{\cdot}}$ (0.17~0.18 eV) and $V_o^{\cdot}$ (0.30~0.33 eV). From J-E characteristics the nonlinear coefficient (${\alpha}$) and resistivity (${\rho}_{gb}$) of pre-breakdown region decreased as 30 to 24 and 5.1 to 0.08 $G{\Omega}cm$ with sintering temperature, respectively. The double Schottky barrier of grain boundaries in ZB(MCo) ($ZnO-Bi_2O_3-Mn_3O_4-Co_3O_4$) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.64 eV at lower temperature to 1.06 eV at higher temperature. It was revealed that a co-doping of Mn and Co in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against an ambient temperature (${\alpha}$-factor= 0.136).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.5
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• pp.368-373
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• 2010

In this study, we have investigated the effects of Cr dopant on the bulk trap levels and grain boundary characteristics of $Bi_2O_3$-based ZnO (ZB) varistor using admittance spectroscopy and dielectric functions (such as $Z^*,\;Y^*,\;M^*,\;{\varepsilon}^*$, and $tan{\delta}$). Admittance spectra show more than two bulk traps of $Zn_i$ and $V_o$ probably in different ionization states in ZnO-$Bi_2O_3-Cr_2O_3$ (ZBCr) system. Three kinds of temperature-dependant activation energies ($E_{bt}'s$) were calculated as 0.11~0.14 eV of attractive coulombic center, 0.16~0.17 eV of $Zn_{\ddot{i}}$, and 0.33 eV of $V_o^{\cdot}$ as dominant bulk defects. The grain boundaries of ZBCr could be electrochemically divided into two types as a sensitive to ambient oxygen i.e. electrically active one and an oxygen-insensitive i.e. electrically inactive one. The grain boundaries were electrically single type under 460 K (equivalent circuit as parallel $R_{gb1}C_{gb1}$) but separated as double one ($R_{gb1}C_{gb1}-R_{gb2}C_{gb2}$) over 480 K. It is revealed that the dielectric functions are very useful tool to separate the overlapped bulk defect levels and to characterize the electrical properties of grain boundaries.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.41 no.5
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• pp.578-585
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• 1996

This experiment was carried out to obtain the basic informations on yield performance and physicochemical quality properties of North Korean rices at southern high altitude area, Unbong and southeren plain area, Iksan. North Korean cultivars showed significant difference in number of spikelets per panicle, percentage of ripened grain and yield between two locations, but not significant in number of panicle per hill and l000-grain weight. The highest contribution to grain yield was the percentage of ripened grain and l000-grain weight at Iksan and Unbong, respectively, The protein, amylose content, alkali digestion value and Mg/K ratio showed larger variation in varieties than that in the locations cultivated. Mg and K revealed highly significant variations in locations, varieties and variety $\times$ location (V$\times$L) interaction. The amylogram characteristics such as initial pasting temperature, peak, breakdown, setback and consistency viscosities showed highly significant variation in locations, varieties and V$\times$L interaction. The physical characteristics of cooked rice such as adhesiveness, gumniness and chewiness also showed highly significant variations in locations, varieties and V$\times$L interaction.

• Electrical & Electronic Materials
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• v.8 no.5
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• pp.611-618
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$+0.6[mol%]Nb$_{2}$O$_{5}$ (0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere(N$_{2}$ gas). Metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100 [.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. According to increase of the frequency as a functional of temperature, all specimens used in this study showed the dielectric relaxation, and the relaxation frequency was above 106 [Hz], it move to low frequency with increasing resistivity of grain. The specimens showed three kinds of conduction mechanisms in the temperature range 25-125 [.deg. C] as the current increased: the region I below 200 [V/cm] shows the ohmic conduction. The region rt between 200 [V/cm] and 2000 [V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000 [V/cm] is dominated by the tunneling effect.fect.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.570-576
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• 1996

Cu films for future ULSI metallization were prepared by partially ionized beam (PIB) deposition and characterized in terms of preferred orientation, grain size, roughness and resistivity. PIB-Cu films were prepared on Si (100) at pressure of $8 \times 10^{-7}$~$1 \times 10^{-6}$ Torr. Effects of acceleration voltage and ionization potential on the properties of PIB-Cu films have been investigated. As the acceleration voltage increased at constant ionization potential of 400 V, the degree of preferred orientation and surface smoothness of the Cu film increased. At the ionization potential of 450 V, the degree of preferred orientation at the acceleration voltage higher than 2 kV decreased and surface roughness increased with acceleration voltage. Grain size of Cu films increased to 1100 $\AA$ initially up to applied acceleration voltage of 1 kV, above which a little increase occurred with the acceleration voltage. There was no indication of impurities such as C, O in all sample. Resistivity of Cu film had the same trends as the surface roughness with acceleration voltage and ionization potential. The increase of electrical resistivity of PIB-Cu films was explained in terms of grain size and surface roughness

• Journal of The Korean Astronomical Society
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• v.11 no.1
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• pp.31-36
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• 1978

Although Serkowski used a single value K=1.15 in representing all the observed interstellar linear polarization curves by his empirical relation $p({\lambda})/P_{max}$=exp (-K $1n^2({\lambda}_{max}/{\lambda})$), where $p_{max}$ is the maximum polarization at wavelength ${\lambda}_{max}$, we have noticed a meaningful variation in K from observations of 72 stars. By comparing K's with $P_{max}/E_{B-V}\;and\;with\;{\lambda}_{max}$, we have examined how the shape of the polarization curve is related with the degree of grain alignment on one hand, and with grain sizes on the other. We have shown that correlations between K, $P_{max}/E_{B-V}\;and\;with\;{\lambda}_{max}$, are consistent with the idea of Davis-Greenstein mechanism for grain alignment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.367-367
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• 2010

Electrical characteristics of Large-grain silicon with Ni-induced crystallization which gate insulator is made of 80 nm $SiO_2$ and 20 nm SiNx was fabricated and measured with different channel widths, channel length fixed $10{\mu}m$. Focusing on the changes of channel widths from $4{\mu}m$ to $40{\mu}m$. Field-effect mobility decreased from 111.30 to $94.10\;cm^2/V_s$ when the channel widths increased. Still threshold voltage was almost similar with -1.06V.

• Journal of Powder Materials
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• v.14 no.1 s.60
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• pp.50-55
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• 2007

The hydrogen sorption speeds of $Zr_{57}V_{36}Ti_7$ amorphous alloy and its crystallized alloys were evaluated at room temperature. $Zr_{57}V_{36}Ti_7$ amorphous alloy was prepared by ball milling. The hydrogen sorption rate of the partially crystallized alloy was higher than that of amorphous. The enhanced sorption rate of partially crystallized alloy was explained in terms of grain refinement that has been known to promote the diffusion into metallic bulk of the gases. The grain refinement could be obtained by crystallization of amorphous phase resulting in the observed increase in sorption property.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.23-30
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• 1997

Semiconductive SrTiO3 ceramic bodies were prepared by conventional ceramic powder processes in-cluding sintering in a reducing atmosphere. Sodium or potassium ions were diffused from the surface of the sintered bodies into the inner region using thermal diffusion process at 800-120$0^{\circ}C$. The effects of such ther-mal treatments on the electrical and chemical characteristics of the grain boundaries were investigated. The presence of sodium or potassium ions at grain boundaries produces non-linear current-voltage behaviors, electrical boundary potential barriers of 0.1-0.2eV, and threshold voltages of 10-70V. The diffused ions form diffusion layers with thicknesses of 20-50nm near the grain boundaries, reducing the concentration of strontium and oxygen.