• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.186-188
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• 1988

Relaxation spectra of the linear dielectric constants $\varepsilon=\varepsilon'-j{\varepsilon}"$ have been measured as functions of temperature and frequency for alternating copolymers of vinylidene cyanide (VDCN/VAc, VDCN/VPr, VDCN/VBz and VDCN/St) It is found that the linear dielectric constants e show characteristics of the temperature dependence that the real part have a large peak related to the glass transition point(Tg), and of the frequency dependence that the real port increases with decreasing frequency and the imaginary part increases largely in low frequency range. These phenomena mean Debye-type relaxation due to the micro-Brownian moi ions of non-crystalline seqments.

• Journal of the Korean Chemical Society
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• v.6 no.1
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• pp.36-46
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• 1962

The author assumes that pure liquid metal is composed of molecular oscillators whose energy states are classified into two subgroups, i.e., A and B states, each being accesible to either one of the two sorts of lattice sites. The partition function involves constants characteristic of substance, which are obtainable from the Debye characteristic temperature assigned to its solid state. Calculation has been made for the various thermodynamic properties such as the vapor pressure, the entropy, and the heat capacity of liquid metals of GroupⅠelements over the temperature range from the melting points to the boiling points. The theoretical values thus obtained are in good accordances with those observed, within experimental error, although a slight derivation is observed in the atomic heat capacity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.739-742
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• 2000

Nanostructured ZnS thin films were grown on the slide glass substrate by the chemical bath deposition using an aqueous so1ution Of ZnSO$_4$and CH$_3$CSNH$_2$at 95$^{\circ}C$. The average grain sizes of the ZnS thin film estimating from the Debye-Scherrer formula are 4.8 nm. The optical transmittance edge of the ZnS thin films (4.0 eV) was shifted to the shelter wavelength compared with that of the bulk ZnS (3.67 eV) due to the quantum size effects. The ZnS thin films showed a strong photoluminescence intensity and a sharp emission band from 410 to 480 nm 3t room temperature. The PWHM of photoluminescence peak was about 40 nm. For the viloet(410 nm) and blue(480 nm) emission of the ZnS thin films, the temperature dependence can be described by an Arrhenius equation with an activation energy of 168 and 157 meV, respectively.

• Korean Journal of Materials Research
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• v.21 no.2
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• pp.73-77
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• 2011

Specific heat of a crystal is the sum of electronic specific heat, which is the specific heat of conduction electrons, and lattice specific heat, which is the specific heat of the lattice. Since properties such as crystal structure and Debye temperature do not change even in the superconducting state, the lattice specific heat may remain unchanged between the normal and the superconducting state. The difference of specific heat between the normal and superconducting state may be caused only by the electronic specific heat difference between the normal and superconducting states. Critical temperature, at which transition occurs, becomes lower than $T_{c0}$ under the influence of a magnetic field. It is well known that specific heat also changes abruptly at this critical temperature, but magnetic field dependence of jump of specific heat has not yet been developed theoretically. In this paper, specific heat jump of superconducting crystals at low temperature is derived as an explicit function of applied magnetic field H by using the thermodynamic relations of A. C. Rose-Innes and E. H. Rhoderick. The derived specific heat jump is compared with experimental data for superconducting crystals of $MgCNi_3$, $LiTi_2O_4$ and $Nd_{0.5}Ca_{0.5}MnO_3$. Our specific heat jump function well explains the jump up or down phenomena of superconducting crystals.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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• pp.85-89
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• 1993

Silicone oil exhibits the properies of both organic and inorganic substances and, thus, it has many superior properties such as higher thermal resistance and lower thermal oxidation level when compared to other dielectric liquids. In order to investigate the dielectric characteristics, dielectric liquids of viscosity 1 [cSt] is chosen as the specimen and experiment is performed in the temperature range of 20∼65 [$^{\circ}C$] and frequency range of 30∼1${\times}$10$\^$6/ [Hz] respectively. As a result, the observed linear decrease in dissipation factor at the frequency range below 3 [kHz] is due to the influence of frequency, whereas the increase in dissipation factor at higher frequency range is contributed by electrode's resistance. At a fixed frequency of 30 [kHz], increasing temperature results in higher peak value and wide width of the absorption curve. This is due to the increase in dipole and viscosity. As temperature increases, dipole moment is decreased from 0.98 to 0.64 [debye]. The activation energy which causes the relaxation and loss of dielectric is obtained about 15 [kcal/mole].

• Electrical & Electronic Materials
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• v.8 no.5
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• pp.587-593
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• 1995

Silicone oils used insulating substances exhibit the both of organic and inorganic properties, and it has many superior characteristics such as the high thermal resistance and low thermal oxidation level when compared to other insulation oils. In order to investigate the dielectric loss due to the increase of viscosity, silicone oils of viscosity 1, 2, 5[cSt] had been chosen as the specimen and experiment has been performed in the temperature range of -70[.deg. C] - 65[.deg. C] and frequency range of 30 - 1*10$\^$5/[Hz]. As a result, the linear decrease of loss at low frequency region in high temperature was due to the influence of applying frequency, whereas the increase of loss at high frequency region was contributed by electrode's resistance. And increasing viscosity, the activation energy increased from 3.77[kcal/mole] to 7.21[kcal/mole]. The dipole moment of specimen was become clear 1.48 - 2.26[debyel in high temperature region(5 - 65[.deg. C]) and 1.05 - 1.80[debye] in low temperature region (-70 - -25[.deg. C])respectively.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.58-63
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• 1995

The crystallographic and magnetic properties of the ferrimagnetic $Ni_{0.5}Co_{0.5}Fe_{2}O_{4}$ have been studied by X-ray and $M\"{o}ssbauer$ measurements. The Crystal structure is found to be spinel structure with the lattice constant $a_{0}=8.346{\pm}0.005\;{\AA}$. $M\"{o}ssbauer$ spectra of $Ni_{0.5}Co_{0.5}Fe_{2}O_{4}$ have been taken at various temperatures rallging from 13 to 780 K. The isomer shifts indicate that the valence states of the Fe ions for tetrahedral(A) and octahedral(B) sites have ferric character. Debye temperatures for the A and B sites are found to be $441{\pm}5\;K$ and $321{\pm}5\;K$, respectively. Atomic migration from the A to the B sites starts near 500 K and increases rapidly with increasing temperature to such a degree that 51 % of the ferric ions at the A sites have moved over to the B sites by 700 K.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.1-6
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• 1999

The crystallographic and magnetic properties of the ferrimagnetic $CoFe_{1.9}Ga_{0.1}O_4$ have been studied by X-ray, M$\"{o}$ssbauer measurements. The crystal structure is found to be inverse spinel structure with the lattice constant $a_0=8.386{\pm}0.005{\AA}$. M$\"{o}$ssbauer spectra of $CoFe_{1.9}Ga_{0.1}O_4$ have been taken at various temperatures ranging from 13 to 840 K. The isomer shifts indicate that the valence states of the Fe ions for tetrahedral (A) and octahedral (B) sites have ferric character. Debye temperatures for the A and B sites are found to be 882$\pm$5 K and 209$\pm$5 K, respectively. Atomic migration form the A to the B sites starts near 350 K and increases rapidly with increasing temperature to such a degree that 73% of the ferric ions at the A sites have moved over to the B sites by 700 K. by 700 K.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.29-34
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• 1999

$Y_{2.5}La_{0.5}Fe_5O_{12}$ is fabricated by a sol-gel method and the magnetic properties of single phase garnet are investigated by using X-ray diffraction, vibrating sample magnetometer, scanning electron microscopy and M$\"{o}$ssbauer spectroscopy. The single phase powders garnet was fired at 100$0^{\circ}C$ for 8 hours. The crystal structures of samples are cubic garnet. Mossbauer spectroscopy were measured from 13 K to 750 K. M$\"{o}$ssbauer spectra show that the iron exist ferric trivalence in sample. The spin wave constants were determined $B_{3/2}=0.32{\pm}0.05,\; C_{5/2}=0.18{\pm}0.05$ and Debye temperature were determined 382 K at 24(d) site and 246 K at 16(a)-site. The saturation magnetization $M_s$ of powder is 25 emu/g. 25 emu/g.

• Journal of the Korean institute of surface engineering
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• v.50 no.3
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• pp.225-229
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• 2017

ZnO nanotubes were synthesized to investigate the effect of wall thickness on the ethanol gas sensing performance. The wall thickness of the nanotubes was varied from approximately 20 to 60 nm. Transmission electron microscopy, X-ray diffraction and SAED (Selected Area Electron Beam Diffraction) analyses showed that the synthesized nanotubes were polycrystalline structured ZnO with the diameter of approximately 200-300nm. The ZnO nanotubes sensor with an optimum wall thickness of 51.8nm showed approximately 8 times higher response, compared to that with 21.14nm wall thick nanotubes, to the ethanol concentration of 500 ppm at the temperature of $300^{\circ}C$. The wall thickness of 51.8nm was found to be a little larger than 46nm, which was theoretically derived Debye length. Along with the study of the wall thickness effect on the performance of the sensors, the mechanisms of gas sensing of the polycrystalline ZnO nanotubes are also discussed.