• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.171-171
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• 2007

Dysprosium-doped bismuth titanate (BDT) thin films were successfully deposited on Pt(111)/Ti/$SiO_2$/Si(100) substrates by liquid delivery MOCVD process and their structural and ferroelectric properties were characterized. Fabricated BDT thin films were found to be random orientations, which were confirmed by X-ray diffraction experiment and scanning electron microscope analysis. The crystallinity of the BDT films was improved and the average grain size increased as the crystallization temperature increased from 600 to $720^{\circ}C$ at an interval of $40^{\circ}C$. The BDT thin film annealed at $720^{\circ}C$ showed a large remanent polarization (2Pr) of $52.27\;{\mu}C/cm^2$ at an applied voltage of 5V. The BDT thin film exhibits a good fatigue resistance up to $1.0{\times}10^{11}$ switching cycles at a frequency of 1 MHz with applied pulse of ${\pm}5\;V$. These results indicate that the randomly oriented BDT thin film is a promising candidate among ferroelectric materials useti비 in lead-free nonvolatile ferroelectric random access memory applications.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.263-270
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• 2012

This study investigates the effect of heat treatment on the mechanical properties of a forged Ni-based superalloy called Nimonic 80A. Nimonic 80A ingot samples were fabricated by vacuum spray casting to achieve a fine and homogenized microstructure. The ingot samples were subsequently hot-forged with the diameter of 220 mm at 1373 K. From the center to the surface of the forged Nimonic 80A, its average grain size decreased and its micro-Vickers hardness increased slightly. Solution treatment was carried out at 1353 K with 8 hours of air cooling followed by aging treatment, which was carried out in the range of 873-1073 K with various times from 0.5 to 256 hours. To set the optimum aging conditions, micro-Vickers hardness tests were performed. The maximum hardness value of 388.0 Hv was obtained by aging at 973 K for 32 hours. Also, tensile tests were performed for optimum aging conditions at room temperature and 873 K. The results can be used effectively to perform reasonable heat treatment of Nimonic 80A superalloy.

• Journal of the Korean institute of surface engineering
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• v.52 no.2
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• pp.78-83
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• 2019

Chloride baths for electrodeposited Ni thin films were fabricated by dissolving metal Ni powders with the mixed solution consisting of HCl and de-ionized water. Current efficiency, residual stress, surface morphology and microstructure of Ni films with the change of metal ion ($Ni^{2+}$) concentrations in the plating solution were studied. Current efficiency was measured to be more than 90% with increasing $Ni^{2+}$ concentrations in the plating solution. Residual stress of Ni thin film was increased from about 400 to 780 MPa with increasing $Ni^{2+}$ concentration from 0.2 to 0.5 M. It is gradually decreased to 650 MPa at 0.9 M $Ni^{2+}$ concentration. Smooth surface morphologies were observed over 0.3 M $Ni^{2+}$ concentration, but nodule surface morphology at 0.2 M. Ni films consist of FCC(111), FCC(200), FCC(220) and FCC(311) peaks in XRD patterns. Preferred orientation of FCC(111) was observed and its intensity was slightly decreased with increasing $Ni^{2+}$ concentration. The average grain size was slightly increased at 0.3 M $Ni^{2+}$ concentration and then slightly decreased with increasing $Ni^{2+}$ concentration.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.383-387
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• 2018

Highly transparent $Y_2O_3$ ceramics were produced using spark plasma sintering (SPS) at $1600^{\circ}C$ and 30 MPa for 5 min. When the SPS process was applied with various amounts of $La_2O_3$ as dopant. The specimen doped with 3 mol% $La_2O_3$ showed the highest density, and rapid particle growth and pore growth occurred, exhibiting that the relative density and average grain size are 99.2% and $17.2{\mu}m$, respectively. The specimen showed excellent transmittance of 79.44% in the visible light region (600 nm), resulting that $La_2O_3$ would be a useful dopant for improving the transmittance and mechanical properties of transparent $Y_2O_3$ ceramics produced with SPS.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.417-423
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• 2010

A dense nanostructured MoSi$_{2}$-SiC composite was synthesized by a pulsed current activated combustion synthesis method within 2 min of one step from mechanically activated powders of Mo$_{2}$C and Si. Simultaneous combustion synthesis and consolidation were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense MoSi$_{2}$-SiC with a relative density of up to 98% was produced under simultaneous application of an 80 MPa pressure and pulsed current. The average grain size and mechanical properties of the composite were investigated.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.603-608
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• 2019

In this study, the multilayered thin films of (Ba,Sr)TiO3/K(Ta,Nb)O3 were fabricated by the sol-gel and spin coating methods, and their structural and electrical properties were investigated. The specimen showed polycrystalline X-ray diffraction (XRD) characteristics with a tetragonal structure. The average grain size and film thickness for one coating were about 30~40nm and 60nm, respectively. The phase transition temperature of specimen was lower than 10 ℃. The dielectric constant and loss at 20 ℃ of the specimen coated six times were 1,231 and 0.69, respectively. The rate of change in dielectric constant at an applied direct current (DC) voltage of the six times coated thin films was 17.3%/V. The electrocaloric effect was the highest around the temperature at which the remanent polarization rapidly changed. When an electric field of 660kV/cm was applied to the triply coated thin films, the highest electrocaloric property of 4.41 ℃ was observed.

• Journal of Ceramic Processing Research
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• v.20 no.4
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• pp.395-400
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• 2019

This study was conducted on the structural and electrical properties of (Ba0.7Sr0.3)TiO3 thin films prepared by the sol-gel and spin-coating methods in order to investigate their applicability to electrocaloric devices. All specimens showed a tetragonal crystal structure and lattice constants of a = 3.972 Å, c = 3.970 Å. The mean grain size of specimens sintered at 800 ℃ was about 30 nm, and the average thickness of 5 times coated specimens was 304~311 nm. In the specimen sintered at 750 ℃, The relative dielectric constant and loss of specimens measured at 20 ℃ were 230 and 0.130, respectively, while dependence of the dielectric constant on unit DC voltage was -8.163 %/V. The remanent polarization and coercive fields were 95.5 μC/㎠ and 161.3 kV/cm at 21 ℃, respectively. And, the highest electrocaloric property of 2.69 ℃ was observed when the electric field of 330 kV/cm was applied.

• Korean Journal of Materials Research
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• v.32 no.10
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• pp.403-407
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• 2022

This research investigated the effect of Si addition on the microstructure, mechanical properties, electric and thermal conductivity of as-extruded Al 6013 alloys. As the content of Si increased, the area fraction of the second phase increased. As the Si content increased, the average grain size decreased remarkably, from 182 (no Si addition) to 142 (1.5Si), 78 (3.0Si) and 77 ㎛ (4.5Si) due to dynamic recrystallization by the dispersed second particles in the aluminum matrix during the hot extrusion. As the Si content increased, the yield strength and ultimate tensile strength increased. The maximum values of yield strength and ultimate tensile strength were 224 MPa and 103 MPa for the 6013-4.5Si alloy. As the amount of Si added increased, the electrical and thermal conductivity decreased. The electrical and thermal conductivity of the Al6013-4.5Si alloy were 44.0 % IACS and 165.0 W/mK, respectively. The addition of Si to Al 6013 alloy had a significant effect on its thermal conductivity and mechanical properties.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.7
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• pp.7-14
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• 2009

In this paper, the effects of annealing conditions on the structural ((002) intensity, FWHM, d-spacing, grain size, (002) peak position), optical (UV peak, UV peak position) and electrical properties (carrier concentrations, resistivity, mobility) of ZnO films were investigated. ZnO films were deposited onto SiO$_2$/si substrates by RF magnetron sputtering from a ZnO target. The substrate was not heated during deposition. ZnO films were annealed in temperature ranges of $500\sim650^{\circ}C$ in the O$_2$ flow for 5$\sim$20 min. The film average thicknesses were in the range of 291 nm. The surface morphologies and structures of the samples were characterize by SEM and XRD, respectively. The optical properties were evaluated by photoluminescence (PL) measurement at room temperature (RT) using a He-Cd 325 nm laser. As the annealing temperature and time vary, the following relations were also observed: (1) proportional relationships among UV intensity (002) intensity, and grain size exist, (2) UV intensity is inversely proportional to FWHM, (3) there is no special relationship between UV intensity and electron carrier concentrations, (4) d-spacing is inversely proportional to (002) peak position, (5) UV peak position in the range of 3.20$\sim$3.24 eV means that ZnO films have a n-type conductivity which was consistent with that obtained from the electrical property, (6) the optimal conditions for the best optical and structural characteristics were found to be oxygen fraction, (O$_2$/(O$_2$+Ar)) of 0.2, RF power of 240W, substrate temperature of RT, annealing condition of 600$^{\circ}C$ for 20 min, and sputtering pressure of 20 mTorr.

• Journal of the Korean earth science society
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• v.40 no.2
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• pp.149-162
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• 2019

In the macro-tide open coast of the Korean western coast, typhoon effects were investigated in terms of variations on topography, surface sediment, and sedimentary environment, which appeared before and after the typhoon Kompasu of 2010. The Kompasu of small size and strong intensity landed on the southwestern coast of the Korean Peninsula and passed across the inland between September 1st and 2nd in 2010. Topography and surface sediments before and after the typhoon were measured and sampled along the survey line of 22 sites in the Gochang Donghori intertidal flat. The intertidal area was divided into high tidal zone, middle tidal zone, and lower tidal zone on the basis of mean high water level, mean sea level, and mean low water level. Topographic variation before and after the typhoon represented deposition of average 0.03 m in high tidal zone, erosion of average -0.15 m in middle tidal zone, and erosion of average -0.39 m in lower tidal zone, respectively. Surface sediments of the intertidal flat consisted mainly of fine to medium sands, and the ratio of fine sand was the largest both before and after the typhoon. Surface sediments after the typhoon became finer in mean grain size showing well sorting rather than those before the typhoon.