• 한국전기전자재료학회논문지
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• 제15권10호
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• pp.896-901
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• 2002

The polarization and strain behavior of multilayer ceramic actuators fabricated by tape casting using a PNN-PZT ceramics were investigated in association with electrode size and internal layer number. Spontaneous polarization and strain decreased with increasing electrode size. In addition, the increase of internal layer number brought reduced spontaneous polarization and increased the field-induced strain. Because the actuators structure is designed to stack ceramic layer and electrode layer alternatively, the ceramic-electrode interfaces may act as a resistance to motion of domain wall. To analyze the effect of ceramic-electrode interface, the diffraction intensity ratio of (002) to (200) planes was calculated from X-ray diffraction patterns of samples subjected to a voltage of 200 V. The diffraction intensity ratio of (002) to (200) planes was decreased with increasing electrode size and internal layer number. The diffraction intensity ratio and straining behavior analyses indicate that the Polarization and strain were affected by the amount of 90°domain decreasing with increasing electrode size and internal layer number. Consequently, the change of polarization and displacement with respect to electrode size and layer number is likely to be caused by readiness of the domain wall movement around the interface.

• Current Applied Physics
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• 제18권11호
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• pp.1205-1211
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• 2018

The frustrated magnet has been regarded as a system that could be a promising host material for the quantum spin liquid (QSL). However, it is difficult to determine the spin configuration and the corresponding mechanism in this system, because of its geometrical frustration (i.e., crystal structure and symmetry). Herein, we systematically investigate one of the geometrically frustrated magnets, the $TbB_4$ compound. Using resonant soft x-ray scattering (RSXS), we explored its spin configuration, as well as Tb's quadrupole. Comprehensive evaluations of the temperature and photon energy/polarization dependences of the RSXS signals reveal the mechanism of spin reorientation upon cooling down, which is the sophisticated interplay between the Tb spin and the crystal symmetry rather than its orbit (quadrupole). Our results and their implications would further shed a light on the search for possible realization of QSL.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.303-303
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• 2015

In order to investigate ion release and biocompatibility of Ti-6Al-4V dental alloy by electrochemical corrosion test and MTT assay, commercial Ti-6Al-4V alloy rod (99.99% Ti, USA, Co) were used in the study. The microstructure of the alloys was examined by optical microscopy (OM), Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), MTT assay, and corrosion test. From the polarization curves, very low current densities were obtained for Ti-6Al-4V alloys, indicating a formation of stable passive layer.

• 한국재료학회지
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• 제25권7호
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• pp.317-321
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• 2015

The effects of Nb doping on the crystal structure, microstructure, and dielectric ferroelectric and piezoelectric properties of $(Bi_{0.5}Na_{0.5})_{0.935}Ba_{0.065}Ti_{(1-x)}Nb_xO_3-0.01SrZrO_3$ (BNBTNb-SZ, with ${\chi}=0$, 0.01 and 0.02) ceramics have been investigated. X-ray diffraction patterns revealed that all ceramics have a pure perovskite structure with tetragonal symmetry. The grain size of the ceramics slightly decreased and a change in grain morphology from square to spherical shape was observed in the Nb-doped samples. The maximum dielectric constant temperature ($T_m$) increases with increasing amount of Nb; however, ferroelectric-relaxor transition temperature ($T_{F-R}$) and maximum dielectric constant (${\varepsilon}_m$) values decrease gradually. Nb addition disrupted the polarization hysteresis loops of the BNBT-SZ ceramics by leading a reduction in the remnant polarization coercive field and piezoelectric constant.

• Corrosion Science and Technology
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• 제3권6호
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• pp.251-256
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• 2004

Exposure of zinc samples in simulated acid rain solution (SARS) was investigated under a periodic wet-dry conditions using an AC impedance technique. The periodic wet and dry exposure consisted of the immersion of zinc samples in SARS for one hour followed by exposure to 7 hours drying at 60% RH. Phases of the corrosion products were indentified by X-ray diffraction (XRD). The influence of relative humdiity (RH), temperature, and surface inclination on the atmospheric corrosion of zinc is described. The reciprocal of polarization resistance (1/Rp) decreases rapidly during the initial stages then slowly and eventually attains a steady state as exposure time progresses. The average of reciprocal of polarization resistance per cycle, (ARPR) was calculated and found to decrease as number of exposure cycle increases. An increase of temperature enhances the corrsion rate of zinc. The values of ARPR, of a sample inclined at 30 o are lower than those for a sample oriented horizontally. The experiment result shows a pronounced dependence of reciprocal of polarization resistance on RH. Exposure in the presence of carbonate anions gives rise to more protective corrosion products than in nitrate anion solution. The corrosion mechanism during the initial stages of atmospheric zinc corrosion under wet-dry cyclic conditions is suggested.

• Corrosion Science and Technology
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• 제22권3호
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• pp.137-152
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• 2023

Polarization behavior and corrosion inhibition of copper in acidic chloride solutions containing benzotriazole were studied. Pourbaix diagrams constructed for copper in NaCl solutions with different BTAH concentrations were used to understand the polarization behavior. Open circuit potential (OCP) depended not only on chloride concentration, but also on whether a CuBTA layer was formed on the copper surface. Only when the (pH, OCP) was located well in the CuBTA region of the Pourbaix diagram, a stable corrosion inhibiting CuBTA layer was formed, which was confirmed by X-ray Photoelectron Spectroscopy (XPS) and a long-term corrosion test. The OCP for the CuBTA layer decreased logarithmically with increasing [Cl^-] activity in the solution. A minimum BTAH concentration required to form a CuBTA layer for a given NaCl concentration and pH were determined from the Pourbaix diagram. It was found that 320 ppm BTAH solution could be used to form a corrosion-inhibiting CuBTA layer inside the corrosion pit in the sprinkler copper tube, successfully reducing water leakage rate of copper tubes. These experimental results could be used to estimate water chemistry inside a corrosion pit.

• Restorative Dentistry and Endodontics
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• 제13권2호
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• pp.221-235
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• 1988

The purpose of this study was to observe characteristic properties through the polarization curves and EMPA images from 4 different types of amalgam obtained by using the potentiostats (EG & G PARC) & EPMA (Jeol JSM-35), to investigate the degree of corrosion of each phase of amalgam on the oxidation peak, and to identify corrosion products from the corroded amalgam by use of X-ray diffractometer(Rigaku). After each amlgam alloy and Hg were triturated as the direction of the manufacturer by means of the mechanical amalgamator(Shofu), the triturated mass was inserted into the cylindrical metal mold which was 12mm in diameter and 10mm in height and was condensed by means of routine manner. The specimen was removed from the mold and stored at room temperature for about 7 days. The standard surface preparation was routinely carried out. Anodic polarization measurement was employed to compare the corrosion behaviours of the amalgams in 0.9% saline solution(pH6.8~7.0) and artificial saliva (pH6.8~7.0) at $37^{\circ}C$. The open circuit potential was determined after 30 minutes' immersion of specimen in electrolyte and the potential scan was begun at the potential of 100mV cathodic from the corrosion potential. The scan rate was 1mV/sec and the surface area of amalgam exposed to the solution was 0.64$cm^2$ for each specimen. All the potentials reported are with respect to a saturated calomel electrode (SCE). EPMA images on the determined oxidation peaks of each amalgam in artificial saliva were observed. X-ray diffraction patterns of each sample were recorded before and after polarization in artificial saliva (Aristaloy, Caulk Spherical, Dispersalloy and Tytin: at +770mV, +585mV, +8.10m V and +680m V respectively) by use of a recording diffractometer. Nickel filtered Cu $K_{{\alpha}_1}$ radiation was used and sample was scanned at $4^{\circ}(2{\theta})/min.$ from $25^{\circ}$ to $80^{\circ}$. The following results were obtained. 1. Oxidation peak potential in artificial saliva shifted to more anodic direction than that in saline solution. 2. The corrosion potential of high copper amalgam was more anodic than the potential of low copper amalgam. 3. The current density was lower in artificial saliva than in saline solution. 4. One of the corrosion products, AgCl was identified by X-ray diffraction analysis. 5. ${\gamma}_2$ phase was the most susceptible to corrosion and e phase was stable in low copper amalgam and ${\eta}$' phase and Ag-Cu eutectic were susceptible to corrosion in high copper amalgam.

• The Korean Journal of Ceramics
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• 제6권4호
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• pp.380-384
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• 2000

Crystal structure of $Ba_5-5X$Y$_10/3$Nb$_10$O$_30$ was tried to determine by Rietveld analysis using powder X-ray diffraction data. This compound has tetragonal tungsten bronze (TTB) structure with general formula, (Al)$_2$(A2)$_4$(B1)$_2$(B2)$_8$(O1)$_8$(O2)$_8$(O3)$_4$(O4)$_2$(O5)$_4$(O6)$_4$. However, it was difficult to determine the distribution of Ba and Y in Al and A2 sites by the analysis only. Combination of Rietveld analysis and site potentials calculation as well as lattice energy calculations helped to determine the distribution. As the result, it was clarified that $Ba^2+$ cations occupy A2 (pentagonal tunnel site) and $Y^3+$ cations occupy Al (cubic site). The distribution of cations at each site coincides with the distribution estimated by the difference of ionic radii. This supports the formation condition of TTB which was proposed in our previous report. $Ba_5-5X$Y$_10X/3$Nb$_10$O$_30$ shows ferroelectric characteristics. In this compound, remanent polarization decreases slightly with the composition X. On the other hand, the result of crystal structure determination reveals that atomic positions along c-axis for A1, A2, B1 and B2 cations are also decreased with the composition X. This would suggest that the dependence of remanent polarization on composition X is derived by the dependence of atomic coordinates on composition X.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.565-568
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• 2001

We have fabricated $Bi_{3.25}$$La_{0.75}$ti$_3$O$_{12}$ (BLT) thin(200nm) films on the Pt/Ti/SiO$_2$/Si substrates using a MOD(Metalorganic decomposition) method with annealing temperature from 55$0^{\circ}C$ to 75$0^{\circ}C$. The structural properties of the films examined by x-ray diffraction. The layered-perovskite phase obtained above $600^{\circ}C$. Scanning electron micrographs showed uniform surface composed of rodlike grains. The grain size increased with increasing annealing temperature. The BLT thin films showed little polarization fatigue test up to 3.5x10$^{9}$ bipolar cycling at a 5V and 100kHz.kHz.

• 한국재료학회지
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• 제28권9호
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• pp.489-494
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• 2018

Lead free $(1-x)(0.675BiFeO_3-0.325BaTiO_3)-xLiTaO_3$ (BFBTLT, x = 0, 0.01, 0.02, and 0.03, with 0.6 mol% $MnO_2$ and 0.4 mol% CuO) were prepared by a solid state reaction method, followed by air quenching and their crystalline phase, morphology, dielectric, ferroelectric and piezoelectric properties were explored. An X-ray diffraction study indicates that lithium (Li) and tantalum (Ta) were fully incorporated in the BFBT materials with the absence of any secondary phases. Dense ceramic samples (> 92 %) with a wide range of grain sizes from $3.70{\mu}m$ to $1.82{\mu}m$ were obtained in the selected compositions ($0{\leq}x{\leq}0.03$) of BFBTLT system. The maximum temperatures ($T_{max}$) were mostly higher than $420^{\circ}C$ in the studied composition range. The maximum values of maximum polarization ($P_{max}{\approx}31.01{\mu}C/cm^2$), remnant polarization ($P_{rem}{\approx}22.82{\mu}C/cm^2$) and static piezoelectric constant ($d_{33}{\approx}145pC/N$) were obtained at BFBT-0.01LT composition with 0.6 mol% $MnO_2$ and 0.4 mol% CuO. This study demonstrates that the high $T_{max}$ and $d_{33}$ for BFBTLT ceramics are favorable for industrial applications.