• 한국세라믹학회지
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• 제36권2호
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• pp.116-121
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• 1999

MgO 단결성 (100) 기판 위에 0.5 wt% Nb 첨가된 전기전도성의 SrTiO3 (Nb:STO) 박막을 Pulsed Laser Deposition 법으로 제조하였다. 산소압력, 타겟과 기판거리, 기판온도, 박막증착시간 등의 박막형성 조건을 다양하게 변화시켜 Nb:STO박막의 격자상수와 박막두께의 변화를 조사하였다. $700^{\circ}C$에서 제작한 0.5 wt% Nb doped SrTiO3 박막의 배향성은 산소분압변화에 따라(100), (110)과 (111)배향이 관찰되었고, 박막제조시의 산소분압이 79.8 Pa로 증가됨에 따라 격자상수는 감소하여 벌크값인 0.390 nm에 근접하였다. 증착시간증가에 따른 박막의 두께는 증착시간에 비례하여 증가하였고, 격자상수의 변화는 거의 없었다. 타겟과 기판사이의 거리가 멀어짐에 따라 박막의 두께는 감소하였으나, 격자상수에는 큰 변화가 없었고 박막두께분포의 균일성이 향상되었다.

• 한국수소및신에너지학회논문집
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• 제16권2호
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• pp.136-141
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• 2005

Li-doped NiO was synthesized by molten salt method. $LiNO_3$-LiOH flux was used as a source for Li doping. $NiCl_2$ was added to the molten Li flux and then processed to make the Li-doped NiO material. Li:Ni ratios were maintained from 5:1 to 30:1 during the synthetic procedure and the Li doping amount of synthesized materials were found between 0.086-0.190 as a Li ion to Ni ion ratio. Li doping did not change the basic cubic structural characteristics of NiO as evidenced by XRD studies, however the lattice parameter decreased from 0.41769nm in pure NiO to 0.41271nm as Li doping amount increased. Hydrogen gas sensors were fabricated using these materials as thick films on alumina substrates. The half surface of each sensor was coated with the Pt catalyst. The sensor when exposed to the hydrogen gas blended in air, heated up the catalytic surface leaving rest half surface (without catalyst) cold. The thermoelectric voltage thus built up along the hot and cold surface of the Li-doped NiO made the basis for detecting hydrogen gas. The linearity of the voltage signal vs $H_2$ concentration was checked up to 4% of $H_2$ in air (as higher concentrations above 4.65% are explosive in air) using Li doped NiO of Li ion/Ni ion=0.111 as the sensor material. The response time T90 and the recovery time RT90 were less than 25 sec. There was minimum interference of other gases and hence $H_2$ gas can easily be detected.

• 한국세라믹학회지
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• 제34권2호
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• pp.139-144
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• 1997

결정학적으로 T' 구조인 Nd2-xCexCuO4-$\delta$ 회토류 구리산화물 초전도체는 지금까지 매우 복잡한 미세구조를 지닌 것으로써 잘 알려져 있다. 이 구리산화물 초전도체가 초전도 특성을 띠려면, Nd3+ 이온이 Ce4+ 이온에 의해 소량 치환되고 동시에 산소환원이 필요하다. 본 연구에서는 투과전자현미경의 수렴성 전자회절(CBED)패턴을 이용하여 Nd2-xCexCuO4-$\delta$ 의 Ce 미량 첨가와 미량의 산소환원에 따른 결정구조의 전이 발생 여부에 관하여 고찰하였다. 세 가지의 서로 다른 시편 Nd2CuO3,Nd1.85Ce0.15CuO4 와Nd1.85Ce0.15CuO3.965을 고상소결에 의하여 만들어 이들 각각 시편에 대한 CBED패턴을 주사투과전자현미경(STEM)으로 관찰하였다. 그리고 실험에 의하여 얻은 이들 HOLZ선들과 컴퓨터 계산에 의해 그려진 이론적인 HOLZ선들과 비교하는 방법에 의하여 Nd1.85Ce0.15CuO4의 격자상수를 구하였다.

• 공업화학
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• 제7권1호
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• pp.34-42
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• 1996

합성에메랄드[$(BeO)_3(Al_{2-x}Cr_xO_3)(SiO_2)_6$]단결정을 flux법에 의하여 육성하였다. 출발물질로 BeO, $Al_2O_3$와 $SiO_2$ 시약을 화학양론비로 혼합하여 사용하였다. 에메랄드 단결정의 성장 조건은 다음과 같다. 온도범위 ; $1150{\sim}900^{\circ}C$, 냉각속도 ; 2, 4, $10^{\circ}C/hr$, 융제 : $Li_2CO_3$, $V_2O_5$, 첨가제 ; $Cr_2O_3$. 에메랄드 단결정의 크기는 2, 4, $10^{\circ}C/hr$의 냉각속도에 의존하였다. 얻어진 에메랄드 단결정을 동정하였고, 그 결과는 다음과 같다. 즉, 결정계 ; 육방정계, 격자상수 ; a=0.921nm, c=0.917nm, 결정의 크기 ; 최대 $0.80{\times}0.95mm^2(c{\times}m)$, 방위 ; c(1000), $m(10{\bar{1}}0)$.

• Journal of Magnetics
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• 제14권4호
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• pp.137-143
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• 2009

The convergence behavior of the all-electron full-potential linearized augmented plane-wave (FLAPW) method with the explicit orthogonalization (XO) scheme is tested on ferromagnetic bulk body-centered-cubic Fe. Applying a commonly used criterion relating the plane-wave and angular momentum cutoffs, $l_{max}\;=\;R_{MT}K_{max}$, where $R_{MT}$ is the muffin-tin (MT) sphere radius and $K_{max}$ is the plane-wave cutoff for the basis - the total energy is converged and stable for $K_{max}R_{MT}$ = 10. The total energy convergence dependence on the star-function cutoff, $G_{max}$, is minimal and so a $G_{max}$ of 3$K_{max}$ or a large enough $G_{max}$ is a reasonable choice. We demonstrate that the convergence with respect to $l_{max}$ or a fixed large enough $G_{max}\;and\;K_{max}$ are independent, and that $K_{max}$ provides a better measure of the convergence than $R_{MT}K_{max}$. The dependence of the total energy on $R_{MT}$ is shown to be small if the core states are treated equivalently, and that the XO scheme is able to treat systems with significantly smaller $R_{MT}$ than the standard LAPW method. For converged systems, the calculated lattice parameter, bulk modulus, and magnetic moments are in excellent agreement with the experimental values.

• 한국세라믹학회지
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• 제42권2호
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• pp.123-126
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• 2005

용매열법으로 출발물질의 농도를 변수로 차여 $BaTiO_3$ 분말을 합성하였다. 평균입자크기는 출발물질의 농도에 따라 비례하였는데 TiO_2를 기준으로 1/16M 농도에tj 59nm이었고 1/2M 농도에서는 89nm까지 증가하였다. 평균입자 크기가 89nm인 BT 분말에 대하여 리트벨트법에 의하여 분석한 결과 상분율은 정방정상 $75.5\%$이었고, 격자상수는 정방정상은 a=0.3999(nm), c=0.40319(nm)이고, 입방정상은 a=0.4015(nm)이었다. 이 분말을 $500^{\circ}C$ 1시간 열처리 후 TEM분석을 한 결과, 분말 내부에 수산 이온들이 거의 존재하지 않음을 확인하였다.

• 한국세라믹학회지
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• 제40권7호
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• pp.620-624
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• 2003

LiCo$_{y}$Mn$_{2-y}$O$_4$ samples were synthesized by calcining a mixture of LiOH.$H_2O$, MnO$_2$ (CMD) and CoCO$_3$ calcining at 40$0^{\circ}C$ for 10 h and then calcining twice at 75$0^{\circ}C$ for 24 h in air with intermediate grinding. All the synthesized samples exhibited XRD patterns for the cubic spinel phase with a space group Fd(equation omitted)m. The electrochemical cells were charged and discharged for 30 cycles at a current density 600 $mutextrm{A}$/$\textrm{cm}^2$ between 3.5 and 4.3 V. As the value of y increases, the size of particles becomes more homogeneous. The first discharge capacity decreases as the value of y increases, its value for y=0.00 being 92.8 mAh/g. The LiMn$_2$O$_4$ exhibits much better cycling performance than that reported earlier. The cycling performance increases as the value of y increases. The efficiency of discharge capacity is 98.9％ for y=0.30. The larger lattice parameter for the smaller value of y is related to the larger discharge capacity. The more quantity of the intercalated and the deintercalated Li in the sample with the larger discharge capacity brings about the larger capacity fading rate.ate.

• 한국세라믹학회지
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• 제27권2호
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• pp.201-210
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• 1990

The mullite-15v/o ZrO2 composites were prepared by dispersing ZrO2-3m/o Y2O3 powders into the mullite matrix in order to improve the mechanical properties of the mullite. The densification and retention of t-ZrO2 in the matrix of synthetic mullite were also investigated. From IR spectroscopic analysis, the obtained amorphous SiO2-Al2O3 powder was observed to have Si-O-Al chemical bond in its structure which might result in the homogeneous mullite composition. The lattice parameter of the mullite powder calcined above 130$0^{\circ}C$ (a0=7.5468$\AA$) is nearly close to the value of stoichiometric mullite (71.8wt% Al2O3, a0=7.5456$\AA$). The sintering behavior, microstructure, flexural strength and fracture toughness of the mullite and mullite-15v/o ZrO2 composites have been studied. The mullite-15v/o ZrO2(+3m/o Y2O3) ceramics with relative densities of 96% were obtained when sintered at 1$600^{\circ}C$. The flexural strength and fractrue toughness of the composites sintered at 1$600^{\circ}C$(calcination temperature of mullite powders ; 125$0^{\circ}C$) had maximum values of 307MPa and 2.50MPa.m1/2, respectively. The fracture toughness improvement in the mullite-ZrO2 cmoposite is assumed to be resulted from the combined effect of the stress-induced phase transformation of tetragonal ZrO2 and the crack deflection due to microcracking by the monoclinic ZrO2 formation.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.397-400
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• 2007

For mapping the distribution of heavy metals in the mining area, field spectroscopy and hyperspectral remote sensing were used in this study. Although heavy metals are spectrally featureless from the visible to the short wave infrared range, possible variations in spectral signal due to heavy metals bound onto minerals can be explained with the metal binding reaction onto the mineral surface. Variations in the spectral absorption shapes of lattice OH and oxygen on the mineral surface due to the combination of heavy metals were surveyed over the range from 420 to 2400 nm. Spectral parameters such as peak ratio and peak area were derived and statistically linked to metal concentration levels in the streambed samples collected from the dry stream channels. The spatial relationships between spectral parameters and concentrations of heavy metals were yielded as well. Based on the observation at a ground level for the relationship between spectral signal and metal concentration levels, the spectral parameters were classified in a hyperspectral image and the spatial distribution patterns of classified pixels were compared with the product of analysis at the ground level. The degree of similarity between ground dataset and image dataset was statistically validated. These techniques are expected to support assessment of dispersion of heavy metal contamination and decision on optimal sampling point.

• 열처리공학회지
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• 제6권4호
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• pp.237-242
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• 1993

The fatigue behaviors of mechanically alloyed Al-4Mg alloys dispersed with either $Al_2O_3$ or $MgAl_2O_4$ oxide particles were investigated. This study maily concerned with the role of coherency of dispersed particles with the matrix on the fatigue behavior of the alloys. The $MgAl_2O_4$ which has a spinel structure with the lattice parameter of exactly the twice of Al showed the habit relation with the matrix. The mechanically alloyed Al-4Mg alloys showed stable stress responses with fatigue cycles from start to failure regadless of strain amplitudes and of existence of dispersoids. The Al-4Mg alloy dispersed with $MgAl_2O_4$ showed not only the better static mechanical properties but also the better low cycle fatigue resistance than that with $Al_2O_3$, i.e., much higher plastic strain energy dissipated to failure, at low strain amplitude. However, this alloy showed inferior fatigue resistance to that dispersed with $Al_2O_3$ or that without dispersion at high strain amplitude. These results imply that $MgAl_2O_4$ may promote lowering the stacking fault energy of the alloy inherited from the coherency with the matrix so that dislocations shuttle back and forth on the same slip plane without cross slipping to other planes during fatigue at low strain amplitude resulting in long fatigue life.