• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.12
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• pp.955-961
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• 2011

We investigated the physical properties of stoichiometric and non-stoichiometric oxide doped complex perovskite, $Ba(Zn_{1/3}Ta_{2/3})O_3$ ceramics and their impacts on the microwave dielectric performances using various characterization techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and network analyzer. According to the measurement of lattice constant changes, anomalous lattice volume contraction of $ZrO_2$ doped $Ba(Zn_{1/3}Ta_{2/3})O_3$ sample only showed the dielectric quality factor enhancements, which was due to the lattice volume contraction as well as the 1:2 B-site cation ordering. In addition, NiO doping was useful to the stabilization of temperature coefficient of resonance frequency.

• Journal of the Korean Chemical Society
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• v.51 no.4
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• pp.339-345
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• 2007

Urea reacts with PtCl2, H2[PtCl6]·6H2O, H2[IrCl6] and Ni(CH3CO2)2 in aqueous solution at high temperature (60-80 °C) yielding [PtCl2(Urea)]·2H2O (1), (NH4)2[PtCl6] (2), (NH4)2[IrCl6]·H2O (3) and [Ni2(OH)2(NCO)2(H2O)2] (4) complexes, respectively. In complex 1, urea coordinates to Pt(II) as a neutral bidentate ligand via amido nitrogen atoms. In complexes 2, 3 and 4 it seems that the coordinated urea molecules decompose during the reaction at high temperature and a variety of reaction products are obtained. All complexes were isolated in moderate yields as dark green (1), yellow (2), pale brown (3) and faint green (4) precipitates, respectively. The reaction products were characterized by their microanalysis, IR, 1H and 13C NMR spectra as well as thermal analysis. General mechanisms describing the formation of these complexes were suggested.

• Journal of Powder Materials
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• v.20 no.5
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• pp.332-337
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• 2013

Recently, self-propagating high-temperature synthesis (SHS), related to metallic and ceramic powder interactions, has attracted huge interest from more and more researchers, because it can provide an attractive, energy-efficient approach to the synthesis of simple and complex materials. The adiabatic temperature $T_{ad}$ and apparent activation energy analysis of different thermit systems plays an important role in thermodynamic studies on combustion synthesis. After establishing and verifying a mathematic calculation program for predicting adiabatic temperatures, based on the thermodynamic theory of combustion synthesis systems, the adiabatic temperatures of the NiO/Al aluminothermic system during self-propagating high-temperature synthesis were investigated. The effect of a diluting agent additive fraction on combustion velocity was studied. According to the simulation and experimental results, the apparent activation energy was estimated using the Arrhenius diagram of $ln(v/T_{ad}){\sim}/T_{ad}$ based on the combustion equation given by Merzhanov et al. When the temperature exceeds the boiling point of aluminum (2,790 K), the apparent activation energy of the NiO/Al aluminothermic system is $64{\pm}14$ kJ/mol. In contrast, below 2,790 K, the apparent activation energy is $189{\pm}15$ kJ/mol. The process of combustion contributed to the mass-transference of aluminum reactant of the burning compacts. The reliability of the simulation results was experimentally verified.

• Journal of Environmental Science International
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• v.16 no.12
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• pp.1451-1462
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• 2007

Heavy metal concentrations in the soil were investigated for the abandoned Samkwang metal mine, Cheongyang-Gun, Chungnam Province, Korea. The concentrations of heavy metal(As, Cd, Cu, Ni, Pb, Zn) were determined in mine soils collected at the abandoned mine sites to obtain a general classification and specification of the pollution in this highly polluted region. The results estimated with the normal test and basis statistic on the central tendency and variation showed that the distribution of heavy metal concentration had significantly different at the range of all locations. The range of spatial distribution on the relationship of heavy metal concentration and pH was $4.8{\sim}8.8$ and heavy metal concentration on the type of land use was highest in forest land, and also Ni and Zn in farm and rice field showed the high concentration. The distribution of heavy metal concentration on the depth of a soil showed that the metal concentrations in subsoil were higher than of those in surface soil, while the concentration of Cu and Ni had no significant difference on the depth of soil. Results from the correlation analysis using the data except the extreme and unusual data revel that Zn-Cd(r=0.867), Zn-As(r=0.797), Zn-Pb(r=0.764), Cu-Cd(r=0.673), Cu-As(r=0.614) and Zn-Ni(r=0.605) were the most important parameters in assessing variations of heavy metal in soil. To discriminate pattern differences and similarities among samples, principal factor analysis(PFA) and cluster analysis(CF) were performed using a correlation matrix. This study suggests that PFA and CF techniques are useful tools for identification of important heavy metal and parameters. This study presents the necessity and usefulness of multivariate statistical assessment of complex databases in order to get better information about the quality of soil and gives the basis information to clean up the abandoned mine sites.

• Journal of Electrochemical Science and Technology
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• v.5 no.1
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• pp.32-36
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• 2014

The $0.3Li_2MnO_3{\cdot}0.7LiMn_{0.55}Ni_{0.30}Co_{0.15}O_2$ cathode material was prepared via a co-precipitation method. The vapor grown carbon fiber (VGCF) was used as a conductive material and its effects on electrochemical properties of the $0.3Li_2MnO_3{\cdot}0.7LiMn_{0.55}Ni_{0.30}Co_{0.15}O_2$ cathode material were investigated. From the XRD pattern, the typical complex layered structure was confirmed and a solid solution between $Li_2MnO_3$ and $LiMO_2$ (M = Ni, Co and Mn) was formed without any secondary phases. The VGCF was properly distributed between cathode materials and conductive sources by a FE-SEM. In voltage profiles, the electrode with VGCF showed higher discharge capacity than the pristine electrode. At a 5C rate, 146 mAh/g was obtained compared with 232 mAh/g at initial discharge in the electrode with VGCF. Furthermore, the impedance of the electrode with VGCF did not changed much around $9-10{\Omega}$ while the pristine electrode increased from 21.5${\Omega}$ to $46.3{\Omega}$ after the $30^{th}$ charge/discharge cycling.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.430-436
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• 2000

In this paper, we have studied the effect of constituent ratio NiO, CuO and doped with B-Bi-Zn on proper-ties(microstructure, density, shrinkage, permeability as a function of frequency, etc.) of hexagonal-ferrite for high fre- quency chip-inductor material about several GHz. The permeability were analyzed by impedance analyzer(100 kHz∼ 40 MHz) and network analyzed(30 MHz∼3 GHz). As a result of the characteristics. the B-Bi-Zn glass ceramic was used to lower the sintering temperature for additive as function of frequency from 100kHz to 1.8 GHz showed con-stant tends. The maximum imaginary value of complex permeability was observed near the resonance frequency of 2 GHz.

• Journal of the Korean Chemical Society
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• v.33 no.5
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• pp.510-515
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• 1989

New nickel(II) and coppr(II) complexes of a saturated pentaaza macrobicyclic ligand $[Ni(D)]^{2+},\;[Cu(D)]^{2+},\;and\;[Cu(D)Cl]^+$, where D is 1,3,6,9,12-pentaazabicyclo[10,2,l]pentadecane, have been prepared by the template condensation reaction of tetraethylenepentamine and formaldehyde in the presence of the metal ion. The complexes contain one imidazolidine ring in the macrobicyclic ligand, D. The complexes $[Ni(D)]^{2+}\;and\;[Cu(D)]^{2+}$ have square planar geometry with 5-5-5-6 chelate ring sequence. The electronic spectra of $[Cu(D)Cl]^+$indicate that the complex has square pyramidal geometry. Synthesis, charactrization, and the spectroscopic and chemical properties of the macrobicyclic nickel(II) and copper(II) complexes are described.

• Journal of the Korean Chemical Society
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• v.36 no.1
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• pp.81-86
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• 1992

The electrophilic and nucleophilic reactions of M(S-S,ph)(N-N,H) (M = Ni(II), Pd(II), Pt(II); (S-S,ph) = 1,2-diphenylethylenedithiolate; (N-N,H)=1,10-phenanthroline) complexes have been investigated. Reaction with norbornadiene depended upon the back donating ability of the central metal ion and produced 2,5-dithia-3,4-diphenyl-tricyclo[4,4,1,0]-undeca-3,8-diene. In the reaction with methyl iodide, the effect of cleavage of (N-N,H) ligand affected the yield of methylated $M(S-S,ph)_2$ product. The structure of the thermolysis product, ${\alpha},{\alpha}{\prime}$-bismethylthiostibene $(CH_3S-SCH_3,ph)$ of methylated complexes indicates that the main product of the nucleophilic reaction is $M(CH_3S-SCH_3,ph)(S-S,ph)$. We have synthesized a new mixed-ligand complex M(S-S,CN)(N-N,H)((S-S,CN) = 1,2-dicyanoethylenedithiolate) through the nucleophilic reaction of ligand.

• Bulletin of the Korean Chemical Society
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• v.27 no.11
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• pp.1757-1762
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• 2006

A solvent sublation using salphen as a ligand was studied and applied for the determination of trace Ni(II), Co(II) and Cu(II) in water samples. The fundamental study was investigated by a solvent extraction process because the solvent sublation was done by extracting the floated analytes into an organic solvent from the aqueous solution. The salphen complexes of Ni(II), Co(II) and Cu(II) ions were formed in an alkaline solution of more than pH 8 and then they were extracted into m-xylene. It was known that the each metallic ion formed 1 : 1 complex with the salphen and the logarithmic values of extraction constants for the complexes were 3.3 5.1 as an average value. Based on the preliminary study, the procedure was fixed for the separation and concentration of the analytes in samples. Various conditions such as the pH of solutions, the influence of $NaClO_4$, the bubbling rate and time of $N_2$ gas, and the type of organic solvent were optimized. The metal-salphen complexes could be extracted into m-xylene from the solution of more than pH 8, but the pH could be shifted to acidic solution of pH 6 by the addition of $NaClO_4$. In addition, the solvent sublation efficiency of the analytes was increased by adding $NaClO_4$. The recovery of 97-115% was obtained in the spiked samples in which given amounts of 0.3 mg/L Ni(II), 0.8 mg/L Co(II) and 0.04 mg/L Cu(II) were added.

• Current Applied Physics
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• v.18 no.12
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• pp.1577-1582
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• 2018

While controlling the cation contents in perovskite rare-earth nickelate thin films, a metal-to-insulator phase transition is reported. Systematic control of cation stoichiometry has been achieved by manipulating the irradiation of excimer laser in pulsed laser deposition. Two rare-earth nickelate bilayer thin-film heterostructures with the controlled cation stoichiometry (i.e. stoichiometric and Ni-excessive) have been fabricated. It is found that the Ni-excessive nickelate film is structurally less dense than the stoichiometric film, albeit both of them are epitaxial and coherent with respect to the underlying substrate. More interestingly, as a temperature decreases, a metal-to-insulator transition is only observed in the Ni-excessive nickelate films, which can be associated with the enhanced disproportionation of the Ni charge valence. Based on our theoretical results, possible origins (e.g. anti-site defects) of the low-temperature insulating state are discussed with the need of future work for deeper understanding. Our work can be utilized to realize unusual physical phenomena (e.g. metal-to-insulator phase transitions) in complex oxide films by manipulating the chemical stoichiometry in pulsed laser deposition.