• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.382-385
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• 2009

In this study, we studied switching characteristics of germanium selenide(Ge-Se)/silver(Ag) contact formed by photodoping for use in programmable metallization cell devices. We have been investigated the switching characteristics of Ag-doped chalcogenide thin films. Changed resistance range by direction of applied voltage is about $1\;M{\Omega}$ $\sim$ hundreds of $\Omega$. The cause of these resistance change can be thought the same phenomenon such as resistance variation of PMC-RAM. The results imply that the separated Ag-ions react the atoms or defects in chalcogenide thin films.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.95-98
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• 1998

We have developed new type of superconducting-superionic conducting nanohybrids, $Ag_xI_wBi_2Sr_2Ca_{n-1}Cu_nO_y$ (n=1 and 2) by applying the chimie douce reaction to the superconducting Bi-based cuprates. These nanohybrids can be achieved by the stepwise intercalation whereby the $Ag^+$ ion is thermally diffused into the pre-intercalated iodine sublattice of $IBi_2Sr_2Ca_{n-1}Cu_nO_y$. According to the X-ray diffraction analysis, the Ag-I intercalates are found to have an unique heterostructure in which the superionic conducting Ag-I layer and the superconducting $IBi_2Sr_2Ca_{n-1}Cu_nO_y$ layer are regularly interstratified with a remarkable basal increment of ~7.3$\AA$. The systematic XAS studies demonstrate that the intercalation of Ag-I accompanies the charge transfer between host and guest, giving rise to a change in hole concentration of $CuO_2$ layer and to a slight $T_c$ change. The Ag K-edge EXAFS result reveals that the intercalated Ag-I has a $\beta$-AgI-like local structure with distorted tetrahedral symmetry, suggesting a mobile environment for the intercalated $Ag^+$ ion. In fact, from ac impedance analyses, we have found that the Ag-I intercalates possess a fast ionic conductivity ($\sigma_i=10^{-1.4}\sim 10^{-2.6}\Omega^{-1}\textrm{cm}^{-1}\;at\;270^{\circ}C$ with an uniform activation energy ($\DeltaE_a=0.22\pm 0.02$ eV). More interesting finding is that these intercalates exhibit high electronic conducting as well as ionic ones ($t_i$=0.02~0.60) due to their interstratified structure consisting of superionic conducting and superconducting layers. In this respect, these new intercalates are expected to be useful as an electrode material in various electrochemical devices.

• Bulletin of the Korean Chemical Society
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• v.22 no.1
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• pp.30-36
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• 2001

The crystal structures of fully dehydrated $Pd^{2+}$ - and $TI^{+}$ -exchanged zeolite X, $Pd_{18}TI_{56}Si_{100}Al_{92}O_{384}(Pd_{18}TI_{50-}X$, a = $24.935(4)\AA$ and $Pd_{21}TI_{50}Si_{100}Al_{92}O_{384}(Pd_{21}TI_{50-}X$ a = $24.914(4)\AA)$, have been determined by single-crystal X-ray diffraction methods in the cubic space group Fd3 at $21(1)^{\circ}C.$ The crystals were prepared using an exchange solution that had a $Pd(NH_3)_4Cl_2\;:TINO_3$ mole ratio of 50 : 1 and 200 : 1, respectively, with a total concentration of 0.05M for 4 days. After dehydration at $360^{\circ}C$ and 2 ${\times}$$10^{-6}$ Torr in flowing oxygen for 2 days, the crystals were evacuated at $21(1)^{\circ}C$ for 2 hours. They were refined to the final error indices $R_1$ = 0.045 and $R_2$ = 0.038 with 344 reflections for $Pd_{18}Tl_{56-}X$, and $R_1$ = 0.043 and $R_2$ = 0.045 with 280 reflections for $Pd_{21}Tl_{50-}X$; I > $3\sigma(I).$ In the structure of dehydrated $Pd_{18}Tl_{56-}X$, eighteen $Pd^{2+}$ ions and fourteen $TI^{+}$ ions are located at site I'. About twenty-seven $TI^{+}$ ions occupy site II recessed $1.74\AA$ into a supercage from the plane of three oxygens. The remaining fifteen $TI^{+}$ ions are distributed over two non-equivalent III' sites, with occupancies of 11 and 4, respectively. In the structure of $Pd_{21}Tl_{50-}X$, twenty $Pd^{2+}$ and ten $TI^{+}$ ions occupy site I', and one $Pd^{2+}$ ion is at site I. About twenty-three $TI^{+}$ ions occupy site II, and the remaining seventeen $TI^{+}$ ions are distributed over two different III' sites. $Pd^{2+}$ ions show a limit of exchange (ca. 39% and 46%), though their concentration of exchange was much higher than that of $TI^{+}$ ions. $Pd^{2+}$ ions tend to occupy site I', where they fit the double six-ring plane as nearly ideal trigonal planar. $TI^{+}$ ions fill the remaining I' sites, then occupy site II and two different III' sites. The two crystal structures show that approximately two and one-half I' sites per sodalite cage may be occupied by $Pd^{2+}$ ions. The remaining I' sites are occupied by $TI^{+}$ ions with Tl-O bond distance that is shorter than the sum of their ionic radii. The electrostatic repulsion between two large $TI^{+}$ ions and between $TI^{+}$ and $Pd^{2+}$ ions in the same $\beta-cage$ pushes each other to the charged six-ring planes. It causes the Tl-O bond to have some covalent character. However, $TI^{+}$ ions at site II form ionic bonds with three oxygens because the super-cage has the available space to obtain the reliable ionic bonds.

• Journal of the Korean Magnetics Society
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• v.10 no.3
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• pp.139-142
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• 2000

We present results based on FLAPW local spin density(LSD) calculations of double perovskite structure oxide L $a_2$MnFe $O_{6}$ . The total energy calculations with various spin structures show that this material has a stable ferromagnetic spin configuration. The ionic state of transition metals depend on the spin configuration $_Mn^{4+}$ and F $e^{2+}$ for ferromagnetic structure, M $n^{3+}$ and F $e^{3+}$ for ferrimagnetic structure). It is explained by super exchange interaction between transition metals. The calculated magnetic structure is well matched with recent experimental result.ult.t.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.442-442
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• 2014

Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, is one of the most promising energy-storage devices because of its high power density, super-high cycle life, and safe operation. We herein report a synthesis of graphene-based flexible films by kneading method. Thus, a device can be readily made by sandwiching a polymer membrane included ionic liquid electrolytes between two identical graphene-based flexible films. Devices made with these electrodes exhibit ultrahigh energy density values while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-energy, flexible electronics.

• Journal of the Korean Magnetics Society
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• v.27 no.4
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• pp.140-144
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• 2017

We have studied electronic and magnetic structure of cubane-type Co magnetic molecule using density functional method. The calculated density of states show $Co^{+2}$ ionic state and high-spin state because of large exchange interaction between inside Co 3d electrons. The exchange interaction J between Co atoms depends Co-O-Co angle. The calculated J is ferromagnetic with right angles. On the other hand J is antiferromagnetic with large angles since super-exchange interactions between $Co^{+2}$ atoms. It induces that Co cubane has a antiferromagnetic spin structure of AFM1 = [${\uparrow}{\uparrow}{\downarrow}{\downarrow}$]

• Applied Chemistry for Engineering
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• v.16 no.5
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• pp.648-652
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• 2005

A super ionic conductor, $K^+$-beta-aluminas, which is known to be difficult to obtain in the form of dense sintered density under atmospheric pressure, was pulverized to 350 nm mean particle size using attrition mill. The sample were pressed into tablet form by uniaxial pressing. The specimen was sintered under atmospheric pressure in powder form. Sintering temperature range was $1400^{\circ}C$ to $1650^{\circ}C$ at $50^{\circ}C$ intervals. Additionally, zone sintering was carried out to control the growth grain at high temperature ($1600^{\circ}C$). The density of specimens that were sintered at $1600^{\circ}C$ and $1650^{\circ}C$, and sintered at $1600^{\circ}C$ by zone sintering were about 93% and 95%, respectively. In the case of the lengthened sintering time to 2 h, the density of specimen was reduced to lower than 90%, since the particles were grown to the duplex microstructure.

• Applied Chemistry for Engineering
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• v.20 no.3
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• pp.317-321
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• 2009

In order to analyze the high temperature phase formation and the sinterability of super ionic conductor $K^+-{\beta}/{\beta}"-Al_2O_3$ which is commonly used as a solid oxide electrolyte, the pure $K^+-{\beta}/{\beta}"-Al_2O_3$ powder in the ternary system $K_2O-LiO_2-Al_2O_3$ was synthesized by solid state reaction and formed to tube and disk using slip casting method and cold isostatic pressing (CIP), respectively. The slip casting was conducted in an alumina mold with the slurry containing 40 wt% of solid contents and the CIP was carried out under 20 MPa. The samples were sintered at $1600^{\circ}C$, $1700^{\circ}C$ and $1750^{\circ}C$, respectively, and their phase formation and the sintering density were investigated according to the forming method. The samples produced by CIP showed far higher ${\beta}"-Al_2O_3$ fraction as compared with those by slip casting. On the other hand, the samples by slip casting showed slightly higher sintering density. The relative density reached to about 83% at $1750^{\circ}C$ and for 1 h, independent of the forming method. In the case of 90 min socking time, the density was decreased owing to the exaggerated grain growth and the pores by $K_2O$ evaporation.

• Journal of Korean Society for Atmospheric Environment
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• v.21 no.6
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• pp.675-687
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• 2005

In this study, the cyclone/denuder/filter pack sampling system was used to measure the daily concentrations of water soluble inorganic compounds of fine ($D_{p}< 2.5\;{\mu}m$) and coarse ($D_{p}<10{\mu}m$m) size fractions of aerosol and related gases at Gosan super site during ABC-EAREX 2005. The mean concentrations for $HNO_{3},\;HNO_{2},\;NH_{3}$, were 0.39, 0.08, and $0.29\;{\mu}g/m^3$. respectively. Average concentrations of sulfate, nitrate, and ammonium in $PM_{2.5}$ were 3.39, 1.06, and $1.04\;{\mu}g/m^3$, which occupied about $26\%$ of total $PM_{2.5}$ mass. In particular, more than half of these ionic species were found in size of less than $2.5\;{\mu}m$. Gas phase nitric acid concentrations have shown high correlation coefficient with $HNO_{2}$(R=0.80) and $O_{3}$(R=0.78), implying the active photochemical reactions from its precursors. Equivalent molar ratios between major ion components, $NH_{4}\;^{+}/nss\;SO_4\;^{2-},(0.83\;for\;PM_{2.5},\;0.86\;for\;PM_{10})$, revealed that the existing forms of the secondary aerosols were probably $(NH_{4})_{2}SO_{4}\;and\;(NH_{4})_{3}H\;(SO_{4})_{2}$. Especially, $(NH_{4}\;^{+}+K^{+}+Ca^{2+}+Mg^{2+})/(NO_{3}\;^{-}+nss\;SO_{4}\;^{2-}) (0.99\;for\;PM_{2.5},\;1.05\;for\;PM_{10})$ indicated that some of them existed not only as $NH_{4}NO_{3}$ but also as $CaSO_{4}\;or\;KNO_{3}$, which pointed out the probability of influences from the abundant soil components during Asian dust (AD) periods. These neutralized types of secondary aerosols showed that pollutants could be aged and transported from a distance.

• Journal of the Korean Chemical Society
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• v.55 no.4
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• pp.603-611
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• 2011

Ethoxylacetyl oxime ligands [HL, (1) and $H_2L^1$, (3)] react with copper(II) acetate monohydrate yield octahedral and square planar complexes, respectively. The complexes have been postulated due to elemental analyses, IR, UVVis. spectra, magnetic susceptibility, conductivity and ESR spectra. Molar conductance of the complexes in DMF indicates a non-ionic character. The ESR spectra of [$(L)_2Cu(H_2O)_2$], (2) complex at room temperature and 77K are characteristic of an axial symmetry ($d_{x2-y2}$) with covalent bond character and have a large line width typical of dipolar interactions. However, [$(L^1)Cu$], (4) complex in the solid state showed spectra of marked broadening and loss of hyperfine splitting confirming spinexchange interactions between the copper(II) sites. The spectrum of the doped copper(II) complex at room temperature showed super-hyperfine splitting from coordinated nitrogen atoms and it has an axial type ($d_{x2-y2}$) with covalent bond character and an essentially square-planar arrangement around the copper(II) ion. The spectrum of [$(L^1)Cu$], (4) in frozen methanol at 77K was characteristic of the triplet state of a dimer species and the distance found between the two copper(II) centers was calculated and is equal to 4.8 ${\AA}$.