• Journal of the Korean institute of surface engineering
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• v.56 no.6
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• pp.380-385
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• 2023

In this study, an MPB PMNT system containing 0.05 to 0.10 wt.% BaTiO₃ was synthesized using a traditional chemical method and its pyroelectricity was investigated. Pyroelectricity, dielectricity, and ferroelectricity of the synthesized BaTiO₃-PMNT system were analyzed by heat treatment at 1240~1280 ℃ for 4 hours to evaluate its applicability as a pyroelectric sensor. Unlike the simple ABO₃ ferroelectric, the BaTiO₃-doped PMNT system exhibited phase transition characteristics over a wide temperature range typical of complex perovskite structures. Although no dramatic change could be confirmed depending on the amount of BaTiO₃ added, stable pyroelectricity was maintained near room temperature and over a wide temperature range. When the amount of BaTiO₃ added increased from 0.05BaTiO₃-PMNT to 0.10BaTiO₃-PMNT, the electric field slightly increased from 5.00×10³ kV/m to 6.75×10³ kV/m, and the maximum value of remanent polarization slightly increased from 0.223 C/m² to 0.234 C/m². The pyroelectric coefficients of 0.05BaTiO₃-PMNT and 0.10BaTiO₃- PMNT at room temperature were measured to be ~0.0084 C/m²K and ~0.0043 C/m²K, respectively. The relaxor ferroelectric properties of the BaTiO₃-PMNT system were confirmed by analyzing the plot of K_max/K versus (T-T_max)^γ. The BaTiO₃-doped MPB PMNT system showed a distinct pyroelectric performance index at room temperature, and the values were F_v ~ 0.0362 m²/C, F_d ~ 0.575×10^-4 Pa^-1/2.

• Composites Research
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• v.37 no.2
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• pp.132-138
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• 2024

In this study, a molecular dynamics simulation study was performed to investigate the size-dependent electroelastic properties of single-walled boron nitride nanotubes(BNNT). To describe the elasticity and polarization of BNNT under mechanical loading, the Tersoff potential model and rigid ion approximation were adopted. For the prediction of piezoelectric constants and Young's modulus of BNNTs, piezoelectric constitutive equations based on the Maxwell's equation were used to calculate the strain-electric displacement and strain-stress relationships. It was found that the piezoelectric constants of BNNTs gradually decreases as the radius of the tubes increases showing a nonnegligible size effect. On the other hand, the elastic constants of the BNNTs showed opposites trends according to the equivalent geometrical assumption of the tubular structures. To establish the structure-property relationships, localized configurational change of the primarily bonded B-N bonded topology was investigated in detail to elucidate the BNNT curvature dependent elasticity.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.92-98
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• 2002

To investigate the electrode structural effect on the ferroelectric electron emission, the electric field distribution in a 2-dimensional structure was calculated as a function of upper electrode diameter, and the switching charge density and emission charge were measured simultaneously. The simulation of the electric field distribution showed that an asymmetric electrode structure could cause a stray field on the bare surface of the ferroelectric cathode near the edge of upper electrode. The distance of stray field from the electrode edge increased with increasing ferroelectric thickness, but it did not depend on the upper electrode diameter. The switching charge density increased more on the cathode with smaller upper electrode diameter. This was attributed to the stray field on the bare ferroelectric surface near the electrode edge, because the stray field for the asymmetric ferroelectric cathode enhanced polarization switching near the electrode edge. From the switching charge density, the distance of stray field from the electrode edge was calculated as about 11-14${\mu}{\textrm}{m}$. The threshold voltage of electron emission was 61-68 kV/cm, which was almost 3 times lager than the coercive voltage. The threshold voltage was not determined just by coercive voltage, but by strength and distance of the stray-field, which largely depended on the geometrical structure of ferroelectric cathode.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.85-91
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• 2011

Many protection methods such as surface coating, electric protection, or other methods have been applied to the numerous steel structures widely used in continental and marine areas to control their corrosion, which is done from an economic point of view. Most of these steel structures are primarily protected by coating methods. However, some steel piles under seawater are protected by the electric protection method, that is, either using an impressed current or a sacrificial anode method. Furthermore, environmental contamination may cause a severely corrosive environment, which, in turn, causes the accelerated corrosion of steel structures. Subsequently, coated steel structures could deteriorate more rapidly than the designed lifetime because of the acid rain caused by air pollution, etc. Therefore, a coating of marine paint exposed to seawater, that is, underwater hardening painting, is increasingly required to be fast drying as well as highly corrosion resistant. In this study, five types of underwater hardening paints were prepared with different resin series and additives. Their corrosion and water resistances were investigated using electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements, etc. Even though it is generally accepted that the corrosion resistance of bare steel tends to increase with a shift of the corrosion potential in the noble direction, the corrosion resistance of a sample with a coating exhibited a relatively better tendency when it had a lower corrosion potential in this study. The corrosion current density was also decreased with a decrease in the diffusion limiting current density, which may mean that there is some relationship between corrosion and water resistance. The S sample of the ceramic resin series showed the relatively best corrosion and water resistance among those of samples, while the worst corrosion and water resistance were observed for the R sample of the epoxy resin series. The corrosion and water resistance of those samples tended to deteriorate with an increase in the immersion days, and their corrosion and water resistances were considered to be apparently improved by the types of resin and additives.

• Journal of the Korean Electrochemical Society
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• v.11 no.2
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• pp.89-94
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• 2008

We synthesized and investigated $(La_{0.75}Sr_{0.25})_{1-x}FeO_{3-\delta}$ perovskite oxides having different stoichiomety (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The electrochemical performances of the synthesized powders were investigated by AC impedance spectroscopy. Both the electric conductivity and the electrochemical performance showed the highest properties at the stoichiometry x = 0.02. Finally, we concluded that the variation of A-site deficiency results in the variation of the amount of oxygen vacancy and micro structure, which leads to the variation of electric conductivity and polarization resistance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.37-43
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• 2017

This review investigates the basic principle of physical interactions and failure mechanisms introduced in the materials and inner parts of semiconducting components under electromagnetic pulses (EMPs). The transfer process of EMPs at the semiconducting component level can be explained based on three layer structures (air, dielectric, and conductor layers). The theoretically absorbed energy can be predicted by the complex reflection coefficient. The main failure mechanisms of semiconductor components are also described based on the Joule heating energy generated by the coupling between materials and the applied EMPs. Breakdown of the P-N junction, burnout of the circuit pattern in the semiconductor chip, and damage to connecting wires between the lead frame and semiconducting chips can result from dielectric heating and eddy current loss due to electric and magnetic fields. To summarize, the EMPs transferred to the semiconductor components interact with the chip material in a semiconductor, and dipolar polarization and ionic conduction happen at the same time. Destruction of the P-N junction can result from excessive reverse voltage. Further EMP research at the semiconducting component level is needed to improve the reliability and susceptibility of electric and electronic systems.

• Journal of the Korean Chemical Society
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• v.53 no.1
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• pp.42-50
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• 2009

The dielectric-spectroscopic and ac conductivity studies firstly carried out on layered manganese doped Sodium Lithium Trititanates ($Na_{1.9}Li_{0.1}Ti_3O_7$). The dependence of loss tangent (Tan$\delta$), relative permittivity ($\varepsilon_r$) and ac conductivity ($\sigma_{ac}$) in temperature range 373-723K and frequency range 100Hz-1MHz studied on doped derivatives. Various conduction mechanisms are involved during temperature range of study like electronic hopping conduction in lowest temperature region, for MSLT-1 and MSLT-2. The hindered interlayer ionic conduction exists with electronic hopping conduction for MSLT-3. The associated interlayer ionic conduction exists in mid temperature region for all doped derivatives. In highest temperature region modified interlayer ionic conduction along with the polaronic conduction, exist for MSLT-1, MSLT-2, and only modified interlayer ionic conduction for MSLT-3. The loss tangent (Tan$\delta$) in manganese-doped derivatives of layered $Na_{1.9}Li_{0.1}Ti_3O_7$ ceramic may be due to contribution of electric conduction, dipole orientation, and space charge polarization. The corresponding increase in the values of relative permittivity may be due to increase in number of dipoles in the interlayer space while the corresponding decrease in the values of relative permittivity may be due to the increase in the leakage current due to the higher doping.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.47-53
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• 2003

In this paper, we described the laboratory layout of the optical CT in connection with the measurement of large current based on Magneto-Optic Effects. It was used He-Ne laser for light source and was used PIN-Photodiode for light receiver. The sensing section was organized by winding optical fiber around conductor on the concept that the rotation angle of polarizing axis by Faraday Effect is proportional to the applied current in to conduction. The optical signal passed through optical fiber sensor was induced to analyzer arranged in the direction of $\theta$ for input polarization, and then analyzed its rotation angle and researched on operating characteristics of optical CT for 60[Hz] AC current measurement from l00[A] to 1000[A] was carried out. In this results, the output signals induced linearly with the current and proved that the intensity is increased with increasing turns of fiber through output differences which in accordance with turns of fiber and we verified that there is not only difference of the output with the medium between electric field and optical fiber, but also the lineality. Measuring the references and output intensities of the optical CT, ratio errors were within $\pm$7%. This confirmed that error rate will be improved by each medium and turns.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.11
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• pp.707-711
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• 2014

The $0.99Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3-0.01LaAlO_3$, $0.01LaMnO_3$ or $0.01LaFeO_3$ (0.99BNKT-0.01LA, 0.01LM or 0.01LF) ceramics were prepared by a conventional mixed mothod. The structure and morphology of the lead free ceramics were characterized by XRD (X-ray diffraction) and FE-SEM (field emission scanning electron microscopy). XRD results indicated that the BNKT ceramics modified by LA, LM or LF induced a transition from a ferroelectric tetragonal to a non-polar pseudo-cubic phase, leading to decrease in the remnant polarization ($P_r$) and coercive field ($E_c$) in the P-E hysterisis loops. The effects of the BNKT ceramics modified by La-based $ABO_3$ pervskite structure on the electric-field induced strain were investigated, and the largest normalized unipolar strain ($S_{max}/E_{max}$) was found in BNKT-0.01LF ceramic.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.260-260
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• 2013

Multiferroic materials have attracted much attention due to their fascinating fundamental physical properties and technological applications in magnetic/ferroelectric data-storage systems, quantum electromagnets, spintronics, and sensor devices. Among single-phase multiferroic materials, $BiFeO_3 $ is a typical multiferroic material with a room temperature magnetoelectric coupling in view of high magnetic-and ferroelectric-ordering temperatures (Neel temperature $T_N$~647 K and Curie temperature $T_C$~1,103 K). Rare-earth ion substitution at the Bi sties is very interesting, which induces suppressed volatility of Bi ion and improved ferroelectric properties. At the same time, Fe-site substitution with magnetic ions is also attracting, and the enhanced ferromagnetism was reported. In this study, $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$ (x=0, 0.05 and 0.1) bulk ceramic compounds were prepared by solid-state reaction and rapid sintering. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ or 24 h to produce $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$. The samples were immediately put into an oven, which was heated up to $800^{\circ}C$ nd sintered in air for 30 min. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies).