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변재동,손용선 고려대학교 공학기술연구소 1986 고려대학교 생산기술연구소 생기연논문집 Vol.22 No.1
The effects of excess TiO₂ and sintering atmosphere on the grain growth and on the dielectric properties of SrTiO₃-based boundary layer ceramic capacitors were investigated. The ceramic capacitors were prepared by doping the strontium titanate having excess amount of TiO₂ with 0.3 mole %, Nb₂O₃ and sintering them in inert gas atmosphere (e.g., nitrogen gas atmosphere). Te sintered bodies were annealed at 1100℃ for 20 to 90 min. in air. These ceramics are characterized by the peculiar structure that every semiconductive grain is surrounded by thin insulating layer which is formed by the solidifcation of Ti-rich liquid phase existing at sintering temperature and oxidation of this in the air. These capacitors exhibited excellent dielectric properties. In the present study, SrTiO₃-based boundary layer capacitors having apparent permittivity of 90,000 to 145,000 with loss factor of 1 to 4% measured at 1 ㎑ were obtained. It was also found that the grain growth behavior of SrTiO₃-based ceramics with excess TiO₂ was sensitively affected by the atmosphere and by the preheating before the sintering.
La-Ni-O계 화합물의 상전이 및 전기전도도에 관한 연구
변재동,김진관,김세호,송기영 한국세라믹학회 1992 한국세라믹학회지 Vol.29 No.1
Phase transition and electrical conductivity of homologous series phases Lan+1NinO3n+1 (n=1,2,3, …, $\infty$) have been investigated. These La-Ni-O chemical compounds were synthesized by solid state reaction. The compound LaNiO3 was thermally stable in air only up to about 1120 K and above this temperature decomposed into homologous series phases Lan+1NinO3n+1 and NiO.
La($Ni_{1-x}Cu_$\chi$$)$O_3$계 화합물의 상안정 및 전기적 특성
변재동,선호정,송기영 한국세라믹학회 1991 한국세라믹학회지 Vol.28 No.11
The phase stability and the electrical properties of La(Ni1-$\chi$Cu$\chi$)O3 (X=0.2, 0.4, 0.6, 0.8) have been investigated. The single phases were observed in the compositions of X=0.2, 0.4, and these single phases were stable up to 87$0^{\circ}C$ and 95$0^{\circ}C$ respectively. The electrical properties of these single phase samples showed metallic behavior similar to LaNiO3 from room temperature to the temperature at which the phase was stable.
$SrTiO_3$: $Pr^{3+}$,$Ga^{3+}$의 발광특성
변재동,이용제,장보윤,이현덕,유영문,류선윤 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.8
SrTiO$_3$에 Pr$^{3+}$ 이온, 또는 Pr$^{3+}$ 이온과 Ga$^{3+}$ 이온을 첨가하여 합성한 형광체와 floating zone method로 성장시킨 단결정의 PL 특성을 조사하였다. 분말 형광체와 단결정에서 모두 Ga$^{3+}$ 이온이 함께 첨가되었을 때 적색 발광 세기가 크게 증가하였다. XRF(X-Ray Fluorescence) 측정결과 Ga$^{3+}$ 이온이 함께 첨가되었을 때 SrTiO$_3$결정 격자내의 Pr$^{3+}$ 이온의 농도가 증가하였다. Ga$^{3+}$ 이온이 함께 첨가되었을 때 적색 발광 세기가 증가하는 것은 첨가된 Ga$^{3+}$ 이온이 결정내 발광 center인 Pt$^{3+}$ 이온의 농도가 증가시켰기 때문이며, 또한 Ga$^{3+}$ 이온이 hole trap center로 작용하기 때문인 것으로 생각된다.
WO_3첨가한 TiO_2 후막산소센서의 제조에 관한 연구
변재동 경북대학교 센서기술연구소 1994 연차보고서 Vol.1994 No.-
WO_3를 첨가한 TiO_2를 소성 산소분압을 달리하여 1400 ℃에서 2시간 동안 소성하였다. 소성한 시료에 촉매로 PdCl_2를 첨가하여 후막을 형성하여 500 - 1400 ℃온도 범위에서 전기저항을 측정하였다. 후막 산소센서의 응답특성을 산소분압이 내려갈 수록 안정화되는데 시간이 걸렸다. 반면 측정온도가 올라갈수록 응답특성의 안정화는 빨리 이루어졌다. 소성 산소분압에 따른 저항의 변화를 관찰한 결과측정온도가 낮은 온도에서 높은 온도로 올라갈 수록 기울기가 감소하는 것을 볼 수 있었다. 또한 소성 산소분압에 따른 미세구조 변화는 첨가되는 WO_3양에 따라 서로 크게 변하지 않았으나 소성 산소분압은 10-13atm에서는 그 이상의 산소분압에서 소성한 시편의 결정립의 크기의 약 3배 이상으로 성장하였다. WO_3-doped TiO_2 was sintered at 1400 ℃ for 2hr. with different atmospheres. The electrical resistance of sintered specimen added with PdCl_2 as a catalysis was measured from 500 ℃ to 1400 ℃. Response characteristics of thick film sensor took longer times as the oxygen partial pressure decreased. By the variation of resistance of specimen with the sintering oxygen partial pressure, the slope of resistance with P_(O_2) decreased as the measuring temperature increased, and the grain size of specimen sintered in P_(O_2)=10^-13 atm was 3 times more than that of specimen sintered in more than P_(O_2)=10^-13 atm. This results suggests the relationship of microstructure and electric properties in sensor characteristics.
$WO_3$ 첨가량 변화에 따른 $BaTiO_3-3{(1-x)TiO_2-xWO_3}$ 계의 고주파 유전특성
박찬식,변재동,김왕섭,김경용 한국세라믹학회 1995 한국세라믹학회지 Vol.32 No.4
The effect of WO3 addition on microwave dielectric properties of BaTiO3-3{(1-x)TiO2-xWO3} system was studied. Addition of WO3 to this system resulted in the formation of BaWO4 and Ba2Ti9O20 phases. Both the dielectric constant (K) and the temperature coefficientof resonant frequency (Tf) were decreased with the amount of WO3 addition. The value of Q$\times$f0 was increased as the amount of WO3 was increased up to x=0.0275, and then decreased when x exceeded 0.03. At x=0.0275, this ceramic showed excellent microwave proprties of K=34-35, Q$\times$f0=50,000-53,000, and near zero ppm/$^{\circ}C$ of Tf.