• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1993년도 추계학술대회 논문집
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• pp.6-9
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• 1993

본 연구에서는 소량(lmol%)의 MnO$_2$를 첨가한 Ba(Zn$_{1}$3Ta$_{2}$3)O$_3$에서 미량(x)외 Ba를 결핍 시켜가면서 마이크로파 유전 특성과 소결성, 구조적 특성을 관찰하였다. XRD분석을 통하여 Ba의 부족량이 증가함에 따라 Ba(Zn$_{1}$3/Ta$_{2}$3/)O$_3$B site의 규칙화와 격자 비틀림(Lattice Distortion)이 촉진되었다. 무부하 Q값은 10.5GHz에서 x가 0.01일때 가장 높은 간(8500)을 나타내었으나 이 후에는 급격히 감소하였고 온도 계수는 Ba의 부족량이 중가함에 따라 중가하였고, x가 0.01일때는 약 2ppm/$^{\circ}C$였다.

• 대한화학회지
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• 제32권1호
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• pp.9-14
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• 1988

$La_{1-x}Ca_xFeO_{3-y}$ 계의 perovskite 형의 화합물은 La_2O_3,\;CaCO_3$, 및 Fe(NO-3)_3{\cdot}9H_2O$의 정량적 혼합물은 1100$^{\circ}C$에서 24시간 동안 가열하여 제조하였다. 이 고용체의 결정구조는 모든 조성에서 사방정계였다. X-선 회절분석과 Mohr 염 분석을 통하여 y값이 증가하면 공위배열에 의한 상전이가 일어나며 격자체적은 x값이 증가함에 따라 감소한다는 것을 확인하였다. 비화학양론적 조성 y는 0.0에서 0.5사이의 값을 나타내었다. Mossbauer 분광분석을 298K에서 수행하여 x = 0.75 조성이 높은 닐온도를 갖는다는 것을 확인하였다. 시료의 전기전도도는 $-100{\sim}100^{\circ}C$ 온도범위에서 측정하였다. 활성화 에너지로부터 공위 배열에 기인한 열린 통로를 갖고 있는 시료들은 이온성 전기전도에 의한 기여가 어느 정도 존재하는 것으로 밝혀졌다.

• 한국재료학회지
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• 제21권3호
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• pp.180-185
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• 2011

This study is aimed to increase the activity of cathodic catalysts for PEMFCs(Polymer Electrolyte Membrane Fuel Cells). we investigated the temperature effect of 20wt% Pt/C catalysts at five different temperatures. The catalysts were synthesized by using chemical reduction method. Before adding the formaldehyde as reducing agent, process was undergone for 2 hours at the room temperature (RT), $40^{\circ}C$, $60^{\circ}C$, $80^{\circ}C$ and $100^{\circ}C$, respectively. The performances of synthesize catalysts are compared. The electrochemical oxygen reduction reaction (ORR) was studied on 20wt% Pt/C catalysts by using a glassy carbon electrode through cyclic voltammetric curves (CV) in a 1M H2SO4 solution. The ORR specific activities of 20wt% Pt/C catalysts increased to give a relative ORR catalytic activity ordering of $80^{\circ}C$ > $100^{\circ}C$ > $60^{\circ}C$ > $40^{\circ}C$ > RT. Electrochemical active surface area (EAS) was calculated with cyclic voltammetry analysis. Prepared Pt/C (at $80^{\circ}C$, $100^{\circ}C$) catalysts has higher ESA than other catalysts. Physical characterization was made by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The TEM images of the carbon supported platinum electrocatalysts ($80^{\circ}C$, $100^{\circ}C$) showed homogenous particle distribution with particle size of about 2~3.5 nm. We found that a higher reaction temperature resulted in more uniform particle distribution than lower reaction temperature and then the XRD results showed that the crystalline structure of the synthesized catalysts are seen FCC structure.

• 한국자기학회지
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• 제17권1호
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• pp.30-33
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• 2007

[ $FeIn_2S_4$ ]를 제조하여 뫼스바우어 분광기, X-선 회절기, SQUID 자화율 측정기를 이용하여 결정학적 및 자기적 특성을 연구하였다. 결정구조는 역스피넬 구조로 In 이온은 각각 사면체 자리(A site)와 팔면체 자리(B site)에 동시에 존재하는데 비하여, Fe 이온은 팔면체 자리에만 존재하였다. Curie-Weiss 역자화율에 따른 유효자기모멘트는 $5.09{\mu}_B$였으며, 닐온도($N\'{e}el$ temperature)는 13 K였다. 이와 같이 낮은 닐온도는 팔면체 자리의 $Fe^{2+}(B)-S^2-Fe^{2+}(B)$의 초미세 상호작용이 약하기 때문인 것으로 설명되어진다. 전기사중극자 상호작용의 온도 의존성은 z-축에 따른 결정장 이론으로 설명되어진다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.147-147
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• 2013

Multiferroic material $BiFeO_3$ (BFO) 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 TC ~1,103 K). Rare-earth ion substitution at the Bi sites is very interesting, which induces suppressed volatility of the Bi ion and improved ferroelectric properties. At the same time, the Fe-site substitution with magnetic ions is also attracting, since the enhanced ferromagnetism was reported. In this study, BFO, $Bi_{0.9}Dy_{0.1}FeO_3$ (BDFO), $BiFe_{0.97}Co_{0.03}O_3$ (BFCO) and $Bi_{0.9}Dy_{0.1}Fe_{0.97}Co_{0.03}O_3 $ (BDFCO) compounds were prepared by conventional solid-state reaction and wet-mixing method. 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 $500^{\circ}C$ for 24 h. The samples were immediately put into an oven, which was heated up to 800oC and sintered in air for 1 h. 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). Dy and Co co-doping at the Bi and the Fe sites induce the enhancement of both magnetic and ferroelectric properties of $BiFeO_3$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.738-743
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• 2004

The microwave dielectric properties and their related structural characteristics in solid solutions of (1-x) $Ba(Mg_{1/3}Nb_{2/3})O_3$ -x $La(Mg_{2/3}Nb_{1/3})O_3$ (BLMN) have been investigated by measuring the dielectric constant${\varepsilon}r)$, Q value and temperature coefficient of resonant frequency$({\tau}f)$ and by observing the crystal structure using high resolution transmission electron microscopy (HRTEM). Microwave dielectric properties showed characteristic features for specific composition. Dielectric constant$({\varepsilon}r)$ showed maximum value at the composition which corresponds to the phase boundary between 1:2 ordered and 1:1 ordered structure. The increase in ${\varepsilon}_r$ may be caused by the rattling of ions by incorporating smaller ions and the disordered structure. The variation of temperature coefficient of resonant frequency${{\tau}_f)$ was investigated in terms of oxygen octahedra tilting.

• Journal of Magnetics
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• 제20권4호
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• The Korean Journal of Ceramics
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• 제4권4호
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• pp.394-398
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• 1998

$Pb_{1-x}Sr_x(Mg-{1}2}W_{1}2})O_3$$ ceramics for application in the microwave frequency range were investigated by dielectric constant and X-ray diffraction measurements. The dielectric constant curves showed two concentration dependent characteristics in the $$Pb(Mg-{1}2}W_{1}2})O_3$-rich$ region. As the Sr constant further increases to x=0.3 the dielectric curve levels off. In the concentration range between x=0.4 and x=1 in which dielectric constant dependence on temperature is negligible, it decreases and Qf value increases in the microwave frequency with increasing Sr. The temperature coefficient (${\tau}_{\varepsilon} $) of the dielectric constant changes from the negative to positive value between x=0.9 and x=1. The dielectric constant, Qf and $\tau\varepsilon$ are correlated with tolerance factor(t). From the X-ray diffraction results for $0.1{\le}x{\le}1$ the cell parameter is found to decrease as x increases and B-site ordering is observed in all the composition ranges.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2013년도 임시총회 및 하계학술연구발표회
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• pp.15-16
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• 2013

Magnetization behavior of ultra thin $Fe_xCo_{1-x}$ alloy (where x varies from 0 to 100) has been investigated as functions of composition on Cr (100) substrate by using in situ surface magneto optical Kerr effect (SMOKE). It's always show in plane uniaxial magnetic anisotropy at room temperature (RT) & Low temperature (LT). It is observed that composition dependent coercive force maximum at about 30 at % Co and 70 at % Co atomic ratio and minimum near equiatomic site. The relative magnetic moments as composition variation also show magnetization collapse near equiatomic site. The magnetization behaviors of Fe-Co alloy on Cr (100) due to composition varies are supported the order-disordering as well as structural stability bcc (ferromagnetic)/fcc (anti-ferromagnetic) phase stability magnetism.

• 한국자기학회지
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• 제16권3호
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• pp.178-181
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• 2006

본 연구에선는 수직 Bridgman 법으로 묽은 자성 반도체 $Si_{1-x}Mn_xTe_{1.5} $ 단결정을 성장시켜 Mn의 조성비 변화에 따른 광학적, 전지적, 그리고 자기적 특성을 조사하였다. X-선 회절 실험으로부터 육방정계(hexagonal) 구조임을 확인하였다. 광흡수 측정으로부터 에너지 띠 간격은 조성비 x와 온도 증가에 대하여 감소함을 보였다. 성장시킨 시료의 경우 강자성 특성을 나타내었으며, Curie 온도는 80K 이상이었다. Mn의 조성비가 증가함에 따라 평균 자기 모멘트와 보자력 값은 증가하였다.