• Bulletin of the Korean Chemical Society
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• 제10권1호
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• pp.5-8
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• 1989

Conventional ceramic method has been used to prepare the green phase, $Y_2BaCuO_5$, commonly observed in 90-K superconductor $YBa_2Cu_3O_P{7-{\delta}}$as an impurity phase. The powder X-ray diffraction analysis indicates that $Y_2BaCuO_5$ has an orthorhombic symmetry with lattice parameter of a = 12.2 $\AA$, b = 5.61 $\AA$, and c = 7.14 $\AA.$ The average g-value 2.13 observed in ESR spectrum is attributable to Cu2+ stabilized in $C_{4v}$ field. From the magnetic susceptibility ($\mu$eff = 2.29 BM) and the ESR measurements, it is confirmed that Cu(II) $3d^9$ electrons in $Y_2BaCuO_5$ are localized and can be characterized by Curie-Weiss behavior. Optical reflectance spectrum shows a broad absorption peak around 680 nm due to dxy ${\rightarrow}$ $dx^2-y^2$ eletronic transition.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.976-981
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• 1997

The magnetic susceptibilities of molybdenum ions with 4d1 electronic configuration in the octahedral crystal field were calculated on the basis of ligand field theory. The experimental magnetic susceptibilities for molybdenum ions, which are stabilized at the octahedral site in the perovskite lattice of Ba2ScMoⅤO6 and Sr2YMoⅤO6, were compared with the theoretical ones. We have tried to fit their temperature dependence of magnetic susceptibility with ligand field parameters, spin-orbit coupling constant ζSO, and orbital reduction parameter κ according to intermediate field coupling and strong field theory. Strong field coupling theory could not explain experimental curves without unrealistically large axial ligand field, since it ignores the mixing up between different state via spin-orbit interaction and ligand field. On the other hand, the intermediate field coupling theory could successfully reproduce experimental data in octahedral and trigonal ligand field. The fitting result demonstrates not only the fact that spin-orbit interaction is primarily responsible for the variation of magnetic behavior but also the fact that effective orbital overlap, enhanced by cubic crystal structure, reduces significantly orbital angular momentum as indicated by κ parameter.

• Bulletin of the Korean Chemical Society
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• 제20권9호
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• pp.1005-1009
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• 1999

Wustite with NaCl structure is successfully synthesized in a quartz tube sealed under vacuum ( ≒1×10 -3 torr). Hematite in an evacuated quartz tube progressively loses oxide ion at 1373 K. XRD patterns disclose that α-Fe2O3 is transformed into the Fe3O4 after heat treatment at 1373 K for 32 h, and the poorly crystallized FeO is appeared after heat treatment for 48 h. Finally, α-Fe2O3 is completely transformed into the well crystallized Fe 0.935O after heat treatment for 84 h. The electrical resistivity, ac-susceptibility measurement, Mossbauer spectroscopy, and x-ray absorption spectroscopy corroborate the structural phase transition on the iron oxides prepared in a sealed quartz tube depending on the heating time at 1373 K.

• Bulletin of the Korean Chemical Society
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• 제17권12호
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• pp.1123-1127
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• 1996

Crystalline compound RbV2SeO7, a Rb analogue of KV2SeO7, was synthesized from a hydrothermal reaction of V2O5, V2O3, SeO2, and Rb2CO3 in the mole ratio 3: 1: 15: 6 (in millimoles) at 230℃. RbV2SeO7 crystallizes in an orthorhombic space group Pnma (No. 62) with a=18.444(8), b=5.415(3), c=7.070(4) Å, Z=8. The two structures of KV2SeO7 and RbV2SeO7 are almost the same except that bond lengths in the latter are slightly longer than in the former. The magnetic susceptibility measurement for RbV2SeO7 in the temperature range 4-300 K showed an antiferromagnetic ordering with TN=45 K, higher than that for KV2SeO7 of 27 K. The origin of the magnetic coupling and the different ordering temperatures in the two phases are discussed in relation to the crystal structures.

• Bulletin of the Korean Chemical Society
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• 제21권12호
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• pp.1187-1192
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• 2000

Ternary (Mo-Ru-Pd) and binary (Mo-Ru, Mo-Pd) alloys have been prepared using an Ar arc melting furnace. Mo and the noble metals, Ru and Pd, are the constituents of metallic insoluble residues, which were found in the early days of post-irradiation studies on uranium oxide fuels. In the present study, the structure of the alloys was evaluated using a powder X-ray diffractometer. Unit cell parameters were determined by least squares refinements of powder X-ray diffraction data. Scanning electron microscopic analyses of the surface of the alloys indicated that surface morphology was dependent on the crystallographic structure as well as its composition. Measurements of the magnetic susceptibility of the alloys showed evidence of superconducting transition from 3 to 9.2 K. Among the ternary and binary alloys, the ${\sigma}-phase$ showed the highest superconducting transition temperature,~9.2 K.

• Bulletin of the Korean Chemical Society
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• 제20권11호
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• pp.1313-1318
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• 1999

Lewis bases were employed to control the stoichiometry of ferrite film prepared by light enhanced plating (LEP) technique. When 2,2'-bipyridyl was used as a Lewis base, conversion electron Mosbauer spectroscopy (CEMS) and x-ray powder diffraction (XRD) experiments showed that the main component of the ferrite films was metal-deficient magnetite (Fe3(1-δ)O4). Nonstoichiometry and roughness of LEP films were increased by the addition of 2,2'-bipyridyl. Using ethylenediaminetetraacetate (EDTA) as a Lewis base, produced film that was a mixture of magnetite and Υ-FeO(OH). No low temperature transition (Verwey transition) of magnetite was detected in resistivity and ac-susceptibility measurements for the LEP films. Surface morphology of the LEP films was observed by atomic force microscopy (AFM). The size of dominant particles was about 0.2 μm.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.663-665
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• 1992

The superconducting $YBa_2Cu_4O_8$ was synthesized in oxygen condition at 1 atm. The starting material with 1 : 2 : 4 composition was obtained by pyrolysis of EDTA complex, which was converted to 1-2-3 phase during densification, followed by the 1-2-4 phase recovery at $810^{\circ}C$ . The phase presents were identified by XRD, TG, DTA and AC magnetic susceptibility. Our data indicated that considerable amounts of 1-2-4 phase formed but with the 1 : 2 : 3 phase or possibly 2-4-7 as visible. As the P($O_2$) increased with temperature, impurity peak, CuO ($2{\Theta}$ = 38.8), gradually decrease, and we conclude that the 1-2-4 phase is predominant bulk superconductor under the high oxygen pressure.

• Bulletin of the Korean Chemical Society
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• 제11권3호
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• pp.191-194
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• 1990

High-Tc superconducting materials, $YBa_2Cu_3O_xF_y$ with $x{\leq}6.89\;and\;0.25{\leq}y{\leq}0.35$, were prepared and Studied by X-ray diffraction, magnetic susceptibility and resistivity measurement. Under given conditions, reproducible resistivities were obtained, which increased with increase in the amount of fluorine. The introduced fluorine atoms were found to be localized in pyramidal Cu-O units rather than in Cu-O chains. It is suggested that the localized fluorine atom increases the electronic lolcalization of the superconducting electrons.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.243-248
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• 1995

Single crystal EPR spectra of K12[As2W18O66Cu3(H2O)2]${\cdot}$11H2O exhibit an orientation-dependent fine structure of an S = 3/2 system which is accounted for by the exchange and magnetic dipole interactions among the three Cu2+ ions. The hyperfine structure and the lines from the S = 1/2 manifolds have not been observed. The isotropic exchange parameters determined from the magnetic susceptibility data at 5-300 K are J1 = J2 =-7.8 cm-1. The magnitude of J values suggests that the unpaired electrons on three Cu2+ ions interact through a sequence of six bonds involving two tungsten atoms and three oxygen atoms. The Cu-Cu distance, 4.37 $\AA$, determined from the EPR spectra is considerably smaller than the value from the X-ray crystal structure determination, 4.76 $\pm$ 0.03 $\AA$, indicating that the point-dipole model underestimates the dipolar interaction.

• 한국식물병리학회:학술대회논문집
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• 한국식물병리학회 2003년도 정기총회 및 추계학술발표회
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• pp.67.2-68
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• 2003

A rice cultivar, Taebaegbyeo, is highly resistant to rice blast and moderately resistant to bacterial leaf blight (BLB) caused by Magnaporthe grisea and Xanthomonas oryzae pv. oryzae, respectively. To study the rice disease resistance mechanism, we generated rice deletion M3 mutants by gamma-ray irradiation. Blast and BLB responses of 16,000 M3 mutants were screened by inoculating mixtures of 4 races (KJ-201, H-1113a, KI-313, KI-409) of M. grisea and 3 Korean races of X. oryzae pv. oryzae. We selected so far 21 M3 mutants of Taebaegbyeo showing high susceptibility to the diseases. One of the mutants, KCT-6417, was susceptible to KI-1113a race of M. grisea, suggesting the deletion of a race-specific blast resistance gene in the mutant. To isolate rice genes involved in blast resistance and defense response, we take a PCR-based suppression subtractive hybridization approach using cDNAs of blast-inoculated wild type and the KCT-6417 as a tester and a driver, respectively. Genes specifically expressed in the wild type will be presented. The selected genes would give us a clue to understand mechanism for the race specific resistance and defense responses against M. grisea H-1113a in Taebaegbyeo.