• Bulletin of the Korean Chemical Society
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• v.14 no.1
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• pp.82-86
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• 1993

Two crystal structures of dehydrated $Ag_{3.3}Ca_{4.35}-A ({\alpha} = 12.256(2){\AA})$ and of its ethylene sorption complex (${\alpha} = 12.259(2){\AA}$) have been determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m at 21(l)$^{\circ}$C. Both crystals were dehydrated at 360$^{\circ}$C and $2{\times}10^{-6}$ Torr for 2 days and one crystal was treated with 200 Torr of ethylene at 24(2)$^{\circ}$C. The structures were refined to final error indices, $R_1$=O.065 and $R_2$ = 0.088 with 202 reflections and $R_1$=0.049 and $R_2$ = 0.044 with 259 reflections, respectively, for which I>3${\sigma}$(I). In these structures, all Ag$^+$ and Ca$^{2+}$ ions are located on two and three different threefold axes associated with 6-ring oxygens, respectively. In $Ag_{3.3}Ca_{4.35}-A{\cdot}6.65\;C_2H_4,\;3.3\;Ag^+\;and\;3.35\;Ca^{2+}$ ions are recessed 1.09 ${\AA}$ and 0.21 ${\AA}$, respectively, into the large cavity from the (111) plane at O(3). Each Ag$^+$ and Ca$^{2+}$ ion in the large cavity forms a complex with one $C_2H_4$$^{2+}$ ions and ethylene molecules are longer than those between Ag$^+$ ions and ethylene molecules.

• Bulletin of the Korean Chemical Society
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• v.8 no.2
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• pp.69-72
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• 1987

The structures of dehydrated $Ag_9Cs_3$-A treated with hydrogen gas at three different temperatures have been determined by single-crystal X-ray diffraction techniques. Their structures were solved and refined in the cubic space group Pm3m at 23(1) $^{\circ}C$. All crystals were ion exchanged in flowing streams of aqueous $AgNO_3$/$CsNO_3$ with a mole ratio 1:3.0 to achieve the desired crystal composition. The structures treated with hydrogen at $23^{\circ}C(a=12.288(1)\;{\AA})\;and\;310^{\circ}C(a=12.291(2)\;{\AA})$ refined to the final error indices R1 = 0.091 and R2 = 0.079, and 0.065 and 0.073, respectively, using the 216 and 227 reflections, respectively, for which I >3${\sigma}$(I). In both of these structures, eight $Ag^+$ ions are found nearly at 6-ring centers, and three $Cs^+$ ions lie at the centers of the 8-rings at sites of $D_{4h}$ symmetry. One $Ag^{\circ}atom$, presumably formed from the reduction of a $Ag^+$ ion by an oxide ion of a residual water molecule or of the zeolite framework during the dehydration process, is retained within the zeolite, perhaps in a cluster. In these two structures hydrogen gas could not enter the zeolite to reduce the $Ag^+$ ions because the large $Cs^+$ ions blocked all the 8-windows. However, hydrogen could slowly diffuse into the zeolite and was able to reach and to reduce about half of the $Ag^+$ ions in the structure only at high temperature ($470^{\circ}C$). The silver atoms produced migrated out of the zeolite framework, and the protons generated led to substantial crystal damage.

• Geosciences Journal
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• v.22 no.6
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• pp.939-953
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• 2018

We examined the microfabrics of omphacite and garnet in foliated eclogite to determine the influence of the layered structure on seismic observations in subduction zone. The analyzed eclogite, from the Lanterman Range, northern Victoria Land, Antarctica, is characterized by layering in which the modal abundances of garnet and omphacite vary. For garnet, the low aspect ratios, similar angular distribution of long axes relative to the foliation in both layers, uniform grain size distribution, near-random crystallographic preferred orientations (CPOs), and misorientation angle distributions are indicative of passive behavior during deformation. In contrast, omphacite shows relatively high aspect ratios, a low angle between the long axes of crystals and the foliation, a wide grain-size distribution, and distinctive CPOs, suggesting dislocation creep as the main deformation mechanism. The results of fabric analyses are consistent with strain localization into omphacite or omphacite-rich layers rather than garnet or garnet-rich layers. The single-crystal seismic anisotropy of garnet is very weak ($AV_P=0.2%$, $AV_S=0.5-0.6%$), whereas that of omphacite is much stronger ($AV_P=3.7-5.9%$ and $AV_S=2.9-3.8%$). Seismic anisotropy of the omphacite-rich layers shows an increase of 329% for $AV_P$ and 146% for $AV_S$ relative to the garnet-rich layers. Our results demonstrate the importance of the layered structure in strain localization and in the development of the seismic anisotropies of subducting oceanic crust.

• Bulletin of the Korean Chemical Society
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• v.21 no.9
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• pp.867-874
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• 2000

Two new azobenzene crown ether calix[4]arenes, 10 and 11, were synthesized by two pathways. In the first pathway,two ethoxy nitrobenzene groups were attached to t-butylcalix[4]arenes in a 1,3 position. Subsequent reduction ofthe nitrobenzene group s by metallic zinc in an alkaline solution afforded 10 and 11 in8% and 12%,respectively. In the second pathway,an azobenzene containing two glycolic units was prepared prior connect-ing to t-butylcalix[4]arenes. The yields from the second approach (5%, 8% for 10 and 11, respectively) were lower than those from the former approach. Single crystals of 10 suitable for X-ray crystallography was ob-tained by recrystallization in methanol.Both the X-ray structure and the 1H-NMR spectrum of 10 indicated that the stereoisomer of the azobenzene moiety was trans and the calixarene platform was in cone conformation. 1H NMR spectroscopy suggested that 10 underwent an observable cis-trans isomerization in CDCl3 under room light and upon UV irradiation with cis:trans ratios of 33:67 and 36:64,respectively. Compound 6 which was the precursor of 11showed fluxional behavior and was found to have mixed conformations ofcone and partial cone with a ratio of 47:53 at -30 $^{\circ}C.$ 1H NMR spectrum of 11 suggested that 11 was initially isolated as cis azobenzene with calix[4]arene in cone conformation and underwent conformational interconversion through calix[4]arene annulas in a similar fashion to 6 upon exposing to light. The complexation studies of 10 with picrate salts of Na+ and K+ using 1H NMR spectroscopysuggested that Na+ preferred to bind the cis form of 10 while K+ preferred to bind the trans form. The stereoisomer of the azobenzene unit in 11 changed partially from cis to trans upon complexing with K+.

• Bulletin of the Korean Chemical Society
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• v.10 no.6
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• pp.582-585
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• 1989

Two crystal structures of dehydrated $Sr^{2+}\;and\;Tl^+$ exchanged zeolite A, $Sr_xTl_{12-2x}-A$ (x = 1.6 and 5.45), have been determined by single-crystal X-ray diffraction techniques. Their structures were solved and refined in the cubic space group Pm3m at $21(1)^{\circ}C.$ Both crystals were ion exchanged in flowing streams of mixed $Sr(NO_3)_2\;and\;TlNO_3$ aqueous solution, followed by dehydration at $360^{\circ}C\; and\; 2${\times}$10^{-6}$ Torr for 2 days. Full-matrix least-squares refinements of the dehydrated $Sr_{1.6}Tl_{8.8}-A (a = 12.214(2){\AA})\; and\;Sr_{5.45}Tl{1.1}-A (a=12.291(2){\AA})$ have converged to final error indices, $R_1=0.055\; and\;R_2=0.061$ with 286 reflections, and R1 = 0.072 and R2 = 0.090 with 217 reflections, respectively, for which$\;I\;{>}\;3{\sigma}(I)$. In both structures, all Sr(II) ions are coordinated by three framework oxygens; Sr(II) to O(3) distances are $2.21(2){\AA}\;for\;Sr_{1.6}Tl_{8.8}-A \;and\;2.31(1){\AA} \;for\;Sr_{5.45}Tl_{1.1}-A,$and Tl(I) to O(3) distances are $2.657(6){\AA}\;for\;Sr_{1.6}Tl_{8.8}-A\;and\;2.845(8){\AA}\;for\;Sr_{5.45}Tl_{1.1}-A,$ respectively. In each structure, the angle subtended at Sr(II), O(3)-Sr(II)-O(3) is $118.7(4)^{\circ}\;for\; Sr_{1.6}Tl_{8.8}-A \;and\;120.0(4)^{\circ}\;for\;Sr_{5.45}Tl_{1.1}-A.\;Sr^{2+}$ ions prefer to 6-ring sites and $Tl^+$ ions to 8-ring sites when total number of ions per unit cell is more than 8.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.228-232
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• 2021

Ca_1-xZrO₃:xPr phosphor with perovskite structure was successfully synthesized by using skull melting method. The crystal structure, morphology and optical properties of synthesized phosphor were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet fluorescence reaction and photoluminescence. The XRD results indicated that single crystals of CaZrO₃:Pr³⁺ belongs to orthorhombic perovskite system. The synthesized phosphor could be excited by UV light (254 nm) and the emission spectra results indicated that green luminescence of CaZrO₃:Pr³⁺ due to charge transfer transition ³P₀ → ³H₄, ³P₁ → ³H₅ and ³P₀ → ³H₅ at 506, 536 and 548 nm was dominant.

• Transactions of Materials Processing
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• v.28 no.1
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• pp.43-48
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• 2019

Aluminum nitride (AlN) is used by the semiconductor industry, and is a compound that is required when manufacturing high thermal conductivity. The AlN films with c-axis orientation and thermal conductivity characteristic were deposited by using the Pulsed Laser Deposition (PLD). The AlN thin films were characterized by changing the deposition conditions. In particular, we have researched the AlN thin film deposited under optimal conditions for growth atmosphere. The epitaxial AlN films were grown on sapphire ($c-Al_2O_3$) single crystals by PLD with AlN target. The AlN films were deposited at a fixed temperature of $650^{\circ}C$, while conditions of nitrogen ($N_2$) pressure were varied between 0.1 mTorr and 10 mTorr. The quality of the AlN films was found to depend strongly on the $N_2$ partial pressure that was exerted during deposition. The X-ray diffraction studies revealed that the integrated intensity of the AlN (002) peak increases as a function the corresponding Full width at half maximum (FWHM) values decreases with lowering of the nitrogen partial pressure. We found that highly c-axis orientated AlN films can be deposited at a substrate temperature of $650^{\circ}C$ and a base pressure of $2{\times}10^{-7}Torr$ in the $N_2$ partial pressure of 0.1 mTorr. Also, it is noted that as the $N_2$ partial pressure decreased, the thermal conductivity increased.

• Progress in Superconductivity and Cryogenics
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• v.23 no.2
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• pp.6-9
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• 2021

Heterostructures fabricated by various combinations of van der Waals (vdW) materials enable us to investigate disorder-free physical properties and realize novel functional devices. Superconducting vdW junctions have attracted a lot of attention because of its simple structure without a barrier layer. In superconducting vdW junction, without extra fabrication effort, a natural barrier can be formed, whose character is sensitive to distance and angle of lattice between two superconducting vdW materials. Using high-quality single crystals and the dry transfer technique, we fabricated the vertically stacked NbSe₂/NbSe₂ and FeSe/FeSe vdW junctions and investigated their Josephson junction properties. We found that in the FeSe junctions, Josephson coupling is extremely sensitive to the fabrication conditions, in contrast to the NbSe₂ junctions. We attributed this distinct character of the FeSe junctions to surface instability and small Fermi surface of FeSe.

• Current Applied Physics
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• v.18 no.11
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• pp.1426-1430
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• 2018

High magnetic field effects on the microstructure and magnetic properties of $BaFe_{12}O_{19}$ hexaferrites synthesized hydrothermal method have been investigated. The obtained results indicate that the lattice constant decreases gradually as the magnetic field strength increases, which may be attributed to the lattice distortion resulted from the high magnetic field. Polycrystalline $BaFe_{12}O_{19}$ samples prepared under magnetic field strength at zero and 5 T are single phase. It is found that application of external magnetic field during synthesis can induce orientated growth of the hexaferrite crystals along the easy magnetic axis. The magnetic properties can be effectively regulated by an application of high magnetic fields. It is observed that the $BaFe_{12}O_{19}$ prepared under a 5 T magnetic field exhibits a higher room-temperature saturation magnetization (66.3 emu/g) than that of the sample (43.6 emu/g) obtained without magnetic field. The results can be explained as the enhanced crystalline, improvement of $Fe^{3+}$ ions occupancy and the oriented growth induced by the external magnetic field. The growing orientation of particles gives rise to increased coercivity due to the enhancement in shape anisotropy. It is expected that an application of magnetic field during the formation of magnetic nanoparticles could be a promising technique to modify magnetic properties with excellent performance.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1393-1398
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• 2018

In conventional single-photon emission computed tomography (SPECT), only the photoelectric events in the detectors are used for image reconstruction. However, if the $^{131}I$ isotope, which emits high-energy radiations (364, 637, and 723 keV), is used in nuclear medicine, both photoelectric and Compton scattering events can be used for image reconstruction. The purpose of our work is to perform simulations for Compton SPECT by using the Geant4 application for tomographic emission (GATE). The performance of Compton SPECT is evaluated and compared with that of conventional SPECT. The Compton SPECT unit has an area of $12cm{\times}12cm$ with four gantry heads. Each head is composed of a 2-cm tungsten collimator and a $40{\times}40$ array of CdZnTe (CZT) crystals with a $3{\times}3mm^2$ area and a 6-mm thickness. Compton SPECT can use not only the photoelectric effect but also the Compton scattering effect for image reconstruction. The correct sequential order of the interactions used for image reconstruction is determined using the angular resolution measurement (ARM) method and the energies deposited in each detector. In all the results of simulations using spherical volume sources of various diameters, the reconstructed images of Compton SPECT show higher signal-to-noise ratios (SNRs) without degradation of the image resolution when compared to those of conventional SPECT because the effective count for image reconstruction is higher. For a Derenzo-like phantom, the reconstructed images for different modalities are compared by visual inspection and by using their projected histograms in the X-direction of the reconstructed images.