• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2002.08a
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• pp.70-71
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• 2002

Exchange-coupled cluster of transition-metal ions are relevant to many different scientific areas, ranging from chemistry to solid-state physics, biology, material science and has been the subject of much research in recent years(1,2). Single crystal EPR spectroscopy works as a very effective tool for the measurement of J values for small exchange interactions. This makes EPR technique very suitable for detection of weak exchange coupling transmitted over long distances via extended atomic and melecular bridges. Large polyoxometallates (3) may provide ideal structural environments for the study of interactions between paramagnetic ions. The detailed nature of magnetic interaction (positive sign and magnitude of J~0.006 $cm^{-1}$ /) was clearly determined for di-copper(II) system by single crystal EPR spectroscopy (4). The single-triplet (S-T) transitions are forbidden by different symmetries of the wave functions. However, when the singlet ground state is mixed into triplet states, the S-T transitions can be allowed and observed as weak lines. These weak S-T lines are positioned symmetrically with respect to the main transitions in the distance equals to 2J from the center of the spectrum. This lines allow one to determine the J-value with very high accuracy when │J│ ＜ hv 0.32 $cm^{-1}$ /. Unfortunately, the S-T transitions in the single crystal were detected by EPR method only in a few complexes until now. We have measured single-triplet transition lines for several magnetically coupled cluster systems and determined their J values accurately. The temperature dependency of J was studied by monitoring the changes in S-T.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.683-689
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• 2005

The structural, piezoelectric and ferroelectric properties of $(1-x)(Bi_{0.5}Na_{0.5})TiO_3$ x=0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) ceramics were investigated. A gradual change in the crystal and microstructures with tile increase of $BaTiO_3$ (BT) concentration was observed. The $(Bi_{0.5}Na_{0.5})TiO_3$ (BNT) samples show unusual properties as ferroelectric relaxer materials. We observed a phase transition in BNT solid solutions with BT having normal ferroelectric phase transition. At room temperature, BNT presents a single phase without the morphotropic phase boundary (MPB). In the case of samples doped with $4\~8 mol\%$ BT, rhombohedral-tetragonal MPB was formed and the piezoelectric properties were improved.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.137-141
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• 2010

The $(1-x)La_{0.7}Sr_{0.3}MnO_3(LSMO)/xZnFe_2O_4$(ZFO) (x = 0, 0.01, 0.03, 0.06 and 0.09) composites were prepared by a conventional solid-state reaction method. We investigated the structural properties, magnetic properties and electrical transport properties of (1-x)LSMO/xZFO composites using X-ray diffraction (XRD), scanning electron microscopy (SEM), field-cooled dc magnetization and magnetoresistance (MR) measurements. The XRD and SEM results indicate that LSMO and ZFO coexist in the composites and the ZFO mostly segregates at the grain boundaries of LSMO, which agreed well with the results of the magnetic measurements. The resistivity of the samples increased by the increase of the ZFO doping level. A clear metal-to-insulator (M-I) transition was observed at 360K in pure LSMO. The introduction of ZFO further downshifted the transition temperature (350K-160K) while the transition disappeared in the sample (x = 0.09) and it presented insulating/semiconducting behavior in the measured temperature range (100K to 400K). The MR was measured in the presence of the 10kOe field. Compared with pure LSMO, the enhancement of low-field magnetoresistance (LFMR) was observed in the composites. It was clearly observed that the magnetoresistance effect of x = 0.03 was enhanced at room temperature range. These phenomena can be explained using the double-exchange (DE) mechanism, the grain boundary effect and the intrinsic transport properties together.

• International Journal of Computer Science & Network Security
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• v.21 no.12
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• pp.309-315
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• 2021

The purpose of the article is to analyze the functioning of economic systems in the context of the development of their potential in a circular economy. It is determined that the functioning of economic systems to ensure their sustainability should meet modern challenges and provide for the formation of competitive institutional architecture, the introduction of structural and regulatory innovations, the transition to an innovative model of development. The specific principles of functioning of economic systems include openness, nonlinearity, multivectority, dynamism, emergence, uncertainty about the development of economic processes. It is substantiated that the linear nature of development and equilibrium are not dominant in the functioning of economic systems, and increasing the level of economic efficiency should go hand in hand with minimizing the activities of enterprises, which necessitates the use of circular economy. The main prerequisites for the transition to a circular economy are analyzed. It is determined that the basic concept of the circular economy involves the development of a system of production and consumption, which is based on processing, reuse, repair, product sharing, change of consumption patterns and new business models and systems. The main elements of the circular economy include: a closed cycle, the use of renewable energy sources, systems thinking. The correlation of the principles of sustainable development and the peculiarities of the application of the circular economy is analyzed. It is determined that the circular economy contrasts with the traditional linear economic model, which is based on the model of "take-do-consume-throw away". The advantages and disadvantages due to the use of the principles of circular economy are given. Based on the study, steps are identified to accelerate the transition from a linear economy to a circular economy.

• Korean Journal of Materials Research
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• v.33 no.10
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• pp.400-405
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• 2023

Tb³⁺-doped CaNb₂O₆ (CaNb₂O₆:Tb³⁺) thin films were deposited on quartz substrates at a growth temperature of 300 ℃ using radio-frequency magnetron sputtering. The deposited thin films were annealed at several annealing temperatures for 20 min and characterized for their structural, morphological, and luminescent properties. The experimental results showed that the annealing temperature had a significant effect on the properties of the CaNb₂O₆:Tb³⁺ thin films. The crystalline structure of the as-grown CaNb₂O₆:Tb³⁺ thin films transformed from amorphous to crystalline after annealing at temperatures greater than or equal to 700 ℃. The emission spectra of the thin films under excitation at 251 nm exhibited a dominant emission band at 546 nm arising from the ⁵D₄→⁷F₅ magnetic dipole transition of Tb³⁺ and three weak emission bands at 489, 586, and 620 nm, respectively. The intensity of the ⁵D₄→⁷F₅ (546 nm) magnetic dipole transition was greater than that of the ⁵D₄→⁷F₆ (489 nm) electrical dipole transition, indicating that the Tb³⁺ ions in the host crystal were located at sites with inversion symmetry. The average transmittance at wavelengths of 370~1,100 nm decreased from 86.8 % at 700 ℃ to 80.5 % at an annealing temperature of 1,000 ℃, and a red shift was observed in the bandgap energy with increasing annealing temperature. These results suggest that the annealing temperature plays a crucial role in developing green light-emitting CaNb₂O₆:Tb³⁺ thin films for application in electroluminescent displays.

• Bulletin of the Korean Chemical Society
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• v.25 no.7
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• pp.1051-1054
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• 2004

The structural transformation behavior of $Na_2Ti_3O_7$ by hydrolysis was investigated in mild and strong acidic aqueous medium. Compared with $K_2Ti_4O_9,\;Na_2Ti_3O_7$ exhibits quite different structural and morphological transformation behavior despite their similar layered structural characteristics. $TiO_2(B)$ obtained by heat treatment of $H_2Ti_3O_7\;at\;350^{\circ}C$ transforms to rutile $H_2Ti_3O_7\;at\;900^{\circ}C$. This temperature is much lower than $1200{\circ}C$, the temperature for anatase to rutile transition when $K_2Ti_4O_9$ is used as a starting titanate. A rectangular rod shape and size of $TiO_2(B)$ particles obtained from $Na_2Ti_3O_7$ is also different from a fibrous structure of $TiO_2(B)$ prepared using $K_2Ti_4O_9$. Rutile crystals of 100 nm diameter with a corn-like morphology and large surface area are directly obtained when the hydrolysis of $Na_2Ti_3O_7$ is carried out at $100^{\circ}C$ in a strong acid solution. The structure of starting titanates and the hydrolysis conditions are an important factor to decide the particle size and morphology of $TiO_2(B)\;and\;TiO_2$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.36-44
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• 2003

In this paper, an analytic solution method is proposed to overcome the numerical problems when the slewing dynamics of hybrid coordinate systems is investigated via time finite element analysis. It is shown that the dynamics of the hybrid coordinate systems is governed by the coupled dual differential equations for both slewing and structural modes. Structural modes are transformed into the time-based modal coordinates and analytic spatial propagation equations are derived for each space-dependent time mode. Slew angle history is obtained analytically by appropriate applications of the boundary conditions and structural propagation is re-calculated using the slew angle. Numerical examples are demonstrated to validate the proposed analytic method in comparison to the existing state transition matrix method.

• Journal of the Korean Magnetic Resonance Society
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• v.26 no.1
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• pp.10-16
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• 2022

The phase transition temperatures of CsCoCl₃·2H₂O crystals are investigated via differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Three endothermic peaks at temperatures of 370 K (=T_C1), 390 K (=T_C2), and 416 K (=T_C3) were observed for phase transitions from CsCoCl₃·2H₂O to CsCoCl₃·1.5H₂O, to CsCoCl₃·H₂O, and then to CsCoCl₃·0.5H₂O, respectively. In addition, the spin-lattice relaxation time T_1ρ in the rotating frame and T₁ in the laboratory frame as well as changes in chemical shifts for ¹H and ¹³³Cs near T_C1 were found to be temperature dependent. Our analyses results indicated that the changes of chemical shifts, T_1ρ, and T₁ are associated with structural phase transitions near temperature T_C1. The changes of chemical shifts, T_1ρ, and T₁ near T_C1 were associated with structural phase transitions, owing to the changes in the symmetry of the structure formed of H₂O and Cs⁺ ions. Consequently, the structural symmetry in CsCoCl₃·2H₂O crystals based on temperature is discussed by the environments of their H and Cs nuclei.

• Applied Chemistry for Engineering
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• v.31 no.1
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• pp.97-102
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• 2020

Recently, various degradation mechanisms of lithium secondary battery cathode materials have been revealed. As a result, many studies on overcoming the limitation of cathode materials and realizing new electrochemical properties by controlling the degradation mechanism have been reported. Li-rich layered oxide is one of the most promising cathode materials due to its high reversible capacity. However, the utilization of Li-rich layered oxide has been restricted, because it undergoes a unique atomic structure change during the cycle, in turn resulting in unwanted electrochemical degradations. To understand an atomic structure deterioration mechanism and suggest a research direction of Li-rich layered oxide, we deeply evaluated the atomic structure of 0.4Li₂MnO₃_0.6LiNi_1/3Co_1/3Mn_1/3O₂ Li-rich layered oxide during electrochemical cycles, by using an atomic-resolution analysis tool. During a charge process, Li-rich materials undergo a cation migration of transition metal ions from transition metal slab to lithium slab due to the structural instability from lithium vacancies. As a result, the partial structural degradation leads to discharge voltage drop, which is the biggest drawback of Li-rich materials.

• Journal of the Korean Magnetics Society
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• v.21 no.2
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• pp.43-47
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• 2011

It is known that the Fe-Al transition metal compounds have a lot of disagreement about structural stability and magnetism. In this study, the correlation between magnetism and atomic structure of ordered $B_2$, $L1_2$, and $D0_3$ structured Fe-Al compounds has been investigated using the all-electron full-potential linearized augmented plane wave (FLAPW) method based on the generalized gradient approximation (GGA). We found that considered all the structures were calculated to be stabilized in a ferromagnetic state. The calculated spin magnetic moments of the Fe atoms for B2 and $L1_2$ structures were 0.771 and 2.373 ${\mu}_B$, respectively, and that of Fe(I) and Fe(II) in $D0_3$ structure calculated to be 2.409 ${\mu}_B$, 1.911 ${\mu}_B$, respectively. In order to investigate structural stability between $L1_2$ and $D0_3$ structures, we performed the formation enthalpy calculations. As a result, the $D0_3$ structure is found to be more favorable than $L1_2 one by energy difference 16 meV/atom, which is well consistent with the experimental observation. We understood about structural stability and magnetism for Fe-Al compounds in terms of analysis of their atomic and electronic structures.