• Korean Journal of Crystallography
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• v.11 no.4
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• pp.195-199
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• 2000

Ceramics based on CaTiO₃-NdAlO₃ solid solutions were synthesized in order to study their dielectric microwave properties. Microstructural analysis was performed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using different analytical methods such as energy-dispersive X-ray spectroscopy (EDXS). It was observed that the heating conditions during sintering and cooling strongly affect the microstructural development of CaTiO₃-NdAlO₃-based ceramics. Various types and concentrations of structural defects were identified, for example, dislocations, twins and/or antiphase boundaries. all such defects resulted in a degradation of the dielectric microwave properties, in particular the quality factor Q. Dielectric properties of CaTiO₃-NdAlO₃-based ceramics can be improved by an appropriate thermal treatment of ceramics which results in a decrease in the concentrations of the identified microstructural defects.

• Korean Journal of Crystallography
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• v.3 no.2
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• pp.72-84
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• 1992

The investigation has been carried out for purification, single crystal growth mechanism and convective phenomena in EBFZM of Nb metal. It is found that the EBFZM refined effectively oxygen and nitrogen, the interstitial impurities in Nb, but carbon was increased slightly by backstream of diffusion pump oil. The mechanism of single crystal growth associated with the second recrystallieation in Nb was suggested from the relationship between texture of starting materials and the crystal growth in EBFZM. It was observed from the investigation of convection phenomena in molten zone that the Marangoni convection was dominant in molten zone, which caused the striation in Nb and increased the purification effect of oxygen and nitrogen.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.79-83
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• 2003

The microstructure of bulk electrolytic MnO₂ (EMD) was studied using x-ray diffraction and transmission electron microscopy (TEM). The bulk sample showed a typical powder x-ray diffraction pattern of EMD materials. TEM study showed that the structure of EMD is present at two length scales;grains, ∼0.2 ㎛ in diameter, and ∼10 nm crystallites within the grain. The electron beam microdiffraction study revealed that each grain is an assemblage of multiphase with a common crystallographic orientation, and_that ∼50% of the crystallites are Ramsdellite, ∼30% are ε-MnO₂, and ∼15% are Pyrolusite. The ｛1120｝peak located at about 67° in powder XRD pattern as well as a high-resolution electron microscope (HREM) image of (0001) plane support the existence of ε-MnO₂ phase.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.20-29
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• 1996

Sr0.6Ca0.4CuO2 single crystal has been synthesized by flux method and characterized by the single crystal X-ray diffraction. The compound has the orthorhombic system and the space group is Cmcm(63), lattice parameters are a=3.4645Å, b=16.1417Å, c=3.8727Å. In the (Sr1-xCax)CuO2 compound the limit of Ca from substitution for Sr was determined by the change of bond length. For this, X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDAX) and electron probe micro-analysis (EPMA) were used. From the change of Cu-O bond length as the Ca substitution, we concluded the limit of Ca incorporation Xca≒0.73.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.300-307
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• 2022

Time-resolved serial femtosecond crystallography (TR-SFX) is a powerful technique for determining temporal variations in the structural properties of biomacromolecules on ultra-short time scales without causing structure damage by employing femtosecond X-ray laser pulses generated by an X-ray free electron laser (XFEL). The mixing rate of reactants and biomolecule samples, as well as the hit rate between crystal samples and x-ray pulses, are critical factors determining TR-SFX performance, such as accurate image acquisition and efficient sample consumption. We here develop two distinct sample delivery systems that enable ultra-fast mixing and on-demand droplet injecting via pneumatic application with a square pulse signal. The first strategy relies on inertial mixing, which is caused by the high-speed collision and subsequent coalescence of droplets ejected through a double nozzle, while the second relies on on-demand pneumatic jetting embedded with a 3D-printed micromixer. First, the colliding behaviors of the droplets ejected through the double nozzle, as well as the inertial mixing within the coalesced droplets, are investigated experimentally and numerically. The mixing performance of the pneumatic jetting system with an integrated micromixer is then evaluated by using similar approaches. The sample delivery system devised in this work is very valuable for three-dimensional biomolecular structure analysis, which is critical for elucidating the mechanisms by which certain proteins cause disease, as well as searching for antibody drugs and new drug candidates.

• Korean Journal of Crystallography
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• v.16 no.2
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• pp.81-88
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• 2005

The atoms located at a general position in a crystal do thermally ellipsoidal vibration satisfying 1-fold rotation symmetry. Likewise the thermal vibration of atom at special position must comply with the symmetry of the special position. This paper shows how to calculate the anisotropic temperature factors of the atoms located at special positions.

• Korean Journal of Crystallography
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• v.17 no.1
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• pp.1-5
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• 2006

After the definition of the basis vectors of the two-dimensional direct and reciprocal lattices, various interrelations between them are derived, and additionally how to calculate $\vec{d^*}(hk)//direction\;of\;(hk),\;d(hk)=1/d^*(hk),\;[uv]$, planes belonging to a direction [uv], areas and interplanar spacing of 2-dimensional low different lattices are shown.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.575-580
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• 2014

We uniformly coated Eu(III)- and Tb(III)-doped yttrium oxide onto the surface of $SiO_2$ spheres and then characterized them by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction crystallography and UV-Visible absorption. 2D and 3D photoluminescence image map profiles were reported for the core-shell type structure. Red emission peaks of Eu(III) were observed between 580 to 730 nm and assigned to $^5D_0{\rightarrow}^7F_J$ (J = 0 - 4) transitions. The green emission peaks of Tb(III) between 450 and 650 nm were attributed to the $^5D_4{\rightarrow}^7F_J$ (J = 6, 5, 4, 3) transitions. For annealed samples, Eu(III) ions were embedded at a $C_2$ symmetry site in $Y_2O_3$, which was accompanied by an increase in luminescence intensity and redness, while Tb(III) was changed to Tb(IV), which resulted in no green emission.

• Korean Journal of Crystallography
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• v.14 no.1
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• pp.16-23
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• 2003

The electronic structure and chemical bonding of β-MnO₂ were theoretically investigated by DV-X/sub α/ (the discrete variation X/sub α/) method. which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The calculations on several cluster models having different sizes were carried out for the determination of a model suited for analyzing bulk state. The Mn/sub 15/O/sub 56/ model was selected as a sufficiently suitable model for the calculation of electronic state and chemical bonding by the comparison of the calculated XPS (X-ray photo-electron spectrum) and experimentally measured XPS. By using this model, the electron energy level, the density of state, the bond overlap population, the charge density distribution, and the net ionic transfer between cations and anions were calculated and discussed.

• Korean Journal of Crystallography
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• v.6 no.2
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• pp.69-74
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• 1995

GaAs tilt grain boundaries were propared by growing GaAs epilayers on Ge bicrystals by an organometallic vapor phase epitaxy (OMVPE) method ∑ =9 tilt grain boundaries were produced when two different first-order twin boundaries interacted with one another in GaAs epilayers. Structural investigations were performed for the coherent and second-order twin boundaries of GaAs by high-resolution transmission electron microscopy (HRTEM). Polarities of cross-boundary bondings were determined from the high-order Laue zone (HOLZ) lines in the (200) convergent beam disks : these were recorded from the two grains on either side of the boundaries, respectively, at particular diffraction conditions.