• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.635-638
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• 2004

페로브스카이트 구조를 가지는 $CaZrO_3$ 유전체 세라믹스에 $CaTiO_3$를 부피 비율로 첨가하여 첨가량 변동에 따른 마이크로파 유전 특성을 조사하였다. 또한 저온 동시소성 기능성 LTCC 기판용 유전체 소재로서 활용하기 위하여 저융점의 borosilicate계 유리 프리트를 첨가하여 $CaZrO_3-CaTiO_3$ 복합 유전체 세라믹스의 저온 소결 거동과 마이크로파 유전 특성을 평가하였다. 알칼리가 첨가된 저융점의 borosilicate계 유리 프리트를 $10\sim30$ wt% 범위로 첨가함으로서 $CaZrO_3-CaTiO_3$ 복합 유전체 세라믹스의 소결온도를 $1450^{\circ}C$에서 $900^{\circ}C$이하로 낮출 수 있었으며, 유리 프리트의 첨가량으로 공진 주파수 온도계수 특성을 조절할 수 있었다. 유리 프리트의 첨가량이 15 wt% 첨가시 $875^{\circ}C$에서 충분한 소결이 이루어졌으며, 이 경우 $CaZrO_3-CaTiO_3$ 복합 유전체 세라믹스는 유전율(k) 23, 품질계수(Qxf) 2500, 공진 주파수 온도계수 ($\tau_{cf}$) -3 ppm/$^{\circ}C$의 매우 양호한 마이크로파 유전 특성을 나타내었다. 유리 프리트의 첨가에 의하여 소결 과정에서 주상인 $CaZrO_3$가 $CaZr_4O_9$ 상으로의 변화가 뚜렷이 나타났는데, 이러한 상전이 현상과 함께 미세구조의 변화에 대해서도 고찰하였다.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.171-176
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• 1999

${\gamma}-Fe_2O_3$ thin films on $Al_2O_3$ substrate were prepared by the oxidation of $Fe_3O_4$ thin films processed by PECVD(Plasma-Enhanced Chemical Vapor Deposition) technique. The phase transformation of ${\gamma}-Fe_2O_3$ thin films was mainly controlled by the substrate temperature and oxidation process of $Fe_3O_4$ phase. $Fe_3O_4$ phase was obtained at the deposition temperature of $200{\sim}300^{\circ}C$. $Fe_3O_4$ phase could be transformed into ${\gamma}-Fe_2O_3$ phase under controlled oxidation at $280{\sim}300^{\circ}C$. $Fe_3O_4$ and ${\gamma}-Fe_2O_3$ obtained by oxidation of $Fe_3O_4$ phase had the same spinel structure and were coexisted. The oxidized ${\gamma}-Fe_2O_3$ thin film on $Al_2O_3$ substrate showed a porous island structure.

• Journal of the Mineralogical Society of Korea
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• v.25 no.4
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• pp.283-293
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• 2012

In order to have better insights into the chemical differentiation of Earth from its magma ocean phase to the current stratified structure, detailed information of crystallization kinetics of silicate melts consisting of the magma ocean is essential. The structural transitions in oxide glasses and melts upon crystallization provide improved prospects for a systematic and quantitative understanding of the crystallization processes. Here, we report the $^{27}Al$ 3QMAS NMR spectra for sol-gel synthesized $Al_2O_3$ glass with varying temperature and annealing time. The NMR spectra for the amorphous $Al_2O_3$ show well-resolved Al coordination environments, characterized with mostly $^{[4,5]}Al$ and a minor fraction of $^{[6]}Al$. The fraction of $^{[5]}Al$ in the alumina phase decreases with increasing annealing time at constant temperature. The NMR results of $Al_2O_3$ phases also imply that multiple processes (e.g., crystallization and/or changes in structural disorder within glasses) could involve upon its phase transition. The current results and method can be useful to understand crystallization kinetics of diverse natural and multi-component silicate glasses and melts. The potential result may yield atomic-level understanding of Earth's chemical evolution and differentiation from the magma ocean.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.644-651
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• 1999

In this experiment the Iron phthalocyanine (FePc) films on Si-wafer and alumina pallet were prepared using vacuum sublimation with conditions of changing reaction time, temperature, and deposition rate. Then, some samples were annealed following annealing. Techniques such as XRD, SEM, and resistance measurement method, were dedicated to characterize the changes of surface structure, phase transformation and electric resistance sensitivity in accordance with change of film thickness. In proportion to the decrease of deposition temperature from $370^{\circ}C$ to $350^{\circ}C$, intensities of (200), (011), (211) and (114) planes of $\alpha$-phase were decreased and (100) plane of $\beta$-phase were appeared. The film thickness were controlled by regulating the volume of precursor material during rapid deposition. As a result, it was observed that crystalline particle size had been increased according to the increase of film thickness and $\alpha$-phase transformed to $\beta$-phase. In consequence of measuring the crystallinity of films annealed between $150^{\circ}C$ and $350^{\circ}C$, $\alpha$- to $\beta$-phase transformation was appeared to begin at $150^{\circ}C$ and completely transformed to $\beta$-phase at $350^{\circ}C$. Electric resistance sensitivity of FePc film to $NO_x$ gas along temperature change of FePc films was observed to be more stable with the decrease of the film thickness.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.967-972
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• 2001

The crystal and defect structures of U $O_{x}$(x=2.0, 2.03, 2.14, 2.19, 2.20 and 2.26) were analysed by rietveld refinement and the results were compared to the U-O phase diagram. Neutron diffraction data were collected in the temperature range of RT~100$0^{\circ}C$. The specimens of x=2.14, 2.19, and 2.20 consisted of two phase: $UO_{2+x}$(Fm3m, a≒5.4$\AA$) and $U_4$$O_{9}$(I43d, a≒21.8$\AA$). The proportion of the $UO_{2+x}$(Fm3m) phase increased with increasing the temperature. The variation of the proportion of the two phases with temperature in the U $O_{2.2}$ and U $O_{2.18}$ samples showed some deviation from the expected values from the phase diagram especially at the high temperature range. The phase transitions ${\gamma}$longrightarrow$\beta$longrightarrow$\alpha$ of $U_4$$O_{9}$ were discussed in relation with the phase separation.eparation.ion.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.5
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• pp.431-438
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• 2022

In functional materials, in situ experimental techniques as a function of external stimulus (e.g., electric field, magnetic field, light, etc.) or changes in ambient environments (e.g., temperature, humidity, pressure, etc.) are highly essential for analyzing how the physical properties of target materials are activated/evolved by the given stimulation. In particular, in situ electric-field-dependent X-ray diffraction (XRD) measurements have been extensively utilized for understanding the underlying mechanisms of the emerging electromechanical responses to external electric field in various ferroelectric, piezoelectric, and electrostrictive materials. This tutorial article briefly introduces basic principles/key concepts of in situ electric-field-dependent XRD analysis using a lab-scale XRD machine. We anticipate that the in situ XRD method provides a practical tool to systematically identify/monitor a structural modification of various electromechanical materials driven by applying an external electric field.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.431-434
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• 2001

The mechanical and phase transformation of the cold isostatically pressed $\alpha$-SiC ceramic were investigated as a function of the sintering temperature. The result of phase analysis by XRD revealed 6H, 4H, 3C and phase transformation between 6H and 4H showed a sudden change over 200$0^{\circ}C$. However, the alongrightarrow$\beta$ reverse transformation did not occur to any sintering temperature. The relative density and the mechanical properties of $\alpha$-SiC ceramic was increased with increased sintering temperature. The flexural strength rapidly inclosed below 210$0^{\circ}C$ and showed the highest value of 410 MPa at 220$0^{\circ}C$. This reason is because crack was propagated through surface flaw. The fracture toughness showed the highest value of 3.3 MPa.m$_{1}$2/ at 220$0^{\circ}C$.

• Journal of Conservation Science
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• v.30 no.4
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• pp.395-407
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• 2014

In this study, firing temperature of bricks from the Songsanri tomb complex is interpreted based on the mineralogical and physical changes of soil samples fired at different temperature. When soil samples were burned at 500 to $1,200^{\circ}C$, phase transition of clay minerals affected the mineralogical composition and microstructure, which leaded to alteration of physical features as color, water absorption and porosity. Mineralogical composition can be assumed to vary with the temperature by mineral phase stability, however, color, water absorption, porosity and microstructure had slow change under $1,000^{\circ}C$, and had rapid change from 1,000 to $1,200^{\circ}C$. Upon the mineral and physical alteration of soil, firing temperature of bricks from the Songsanri tomb complex were estimated. Some bricks were over fired at temperature more than $1,200^{\circ}C$, some high-burned bricks were fired from 1,100 to $1,200^{\circ}C$, some bricks were fired by 900 to $1,000^{\circ}C$ and some bricks ere assumed not to be fired. Henceforward mineralogical and physical study can be applied to interpretate more precise firing temperature.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.34-40
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• 2000

The $Pb_{0.94}Y_{0.04}[(Zr_{0.6}Sn_{0.4})_{0.915}Ti_{0.085}]O_3$ ceramics which corresponded to the antiferroelectric-ferroelectric phase boundary composition were prepared for digital-type-piezoelectric/electrostrictive device application. Their dielectric, field-induced polarization (P) and strain (X) behaviors were studied with variations in sintering condition and excess PbO content. The orthorhombic structure of specimens was hardly affected either by excess PbO addition or sintering temperature. With increasing excess PbO content, grains tended to be smaller and rounded ones, and the optimum sintering temperature was lowered. Excess PbO addition stabilized the antiferroelectric phase of the specimen effectively, which was confirmed by P-E and X-E analyses. Also the digital-type-strain character was found to be enhanced despite of slight increase in phase transition (AFE-FE) field and electrical resistivity, and decrease in maximum strain. These results were explained in terms of possible lattice defects and domain wall motion.

• Journal of the Mineralogical Society of Korea
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• v.19 no.2 s.48
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• pp.81-88
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• 2006

The Yttria Partially Stabilized Zirconia powder was prepared by spontaneous precipitation method using $ZrOCl_2{\cdot}8H_O-YCl_33{\cdot}6H_2O$ solution as a starting materials. The optimal experimental conditions such as concentration and pH of starting solutions, the amounts of stabilizer $Y_2O_3$ used, and sintered temperature were carefully studied. The best condition for synthesizing $ZrO_2$ was experimentally selected and applied throughout this study for the preparation of the 3 mole% $Y_2O_3$ partially stabilized zirconia, 3YSZ. The physical properties of 3YSZ was examined by XRD, Raman, DT A, and SEM. The structural transition from pure monoclinic high temperature $ZrO_2$ to tetragonal room temperature 3YSZ was made possible by the added amount of $Y_2O_3$ in the $ZrO_2+Y_2O_3$ system. All Raman Spectrum band appeared in the lower wave numbers rather than in higher wave numbers as structure changes from monoclinic to tetragonal.