서지주요정보
YBCO 박막의 cation disorder와 Bi계 초전도체에서 제2상의 성장 거동 = Cation disorder in YBCO thin film and growth behavior of second phases in Bi system superconductor
서명 / 저자 YBCO 박막의 cation disorder와 Bi계 초전도체에서 제2상의 성장 거동 = Cation disorder in YBCO thin film and growth behavior of second phases in Bi system superconductor / 신동찬.
저자명 신동찬 ; Shin, Dong-Chan
발행사항 [대전 : 한국과학기술원, 1997].
Online Access 비공개원문

소장정보

등록번호

8007409

소장위치/청구기호

학술문화관(문화관) 보존서고

DMS 97017

휴대폰 전송

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초록정보

In part I, $YBa_2Cu_3O_{7-x}$ superconducting thin films have been grown by in situ off-axis RF sputtering with varying oxygen pressure, Ba/Y ratio in a target, and deposition temperature. With decreasing oxygen pressure, increasing Ba/Y ratio, increasing deposition temperature, the critical temperature of thin films decreased and the c-axis length increased. The property change of films with the variation of deposition variables has been explained by a gas phase equilibrium of the oxidation reaction of Ba and Y. Applying Le Chatelier's principle to the oxidation reaction, we were able to predict the relation of deposition variables and the resultant properties of thin films ; the prediction was in good agreement with the experimental results. From the relation between the three deposition variables and gas phase equilibrium, a 3-dim. processing diagram was introduced. This diagram has shown that the optimum deposition condition of $YBa_2Cu_3O_{7-x}$ thin films is not a fixed point but can be varied. The gas phase equilibrium can also be applied to the explanation of previous results that good quality films were obtained at low deposition temperature using active species, such as O, $O_3$ and $O^{2+}$. In part II, the effects of Ag and liquid phase separation on microstructure have been studied in $Bi_2Sr_2CaCu_2O_X$ system. The Ag dissolved in liquid phase made metallic Ag-Cu eutectic phase. Liquid phase in Bi system has a liquid immiscibility gap and separated in two phases : metal liquid which has little oxygen and oxide liquid which has much oxygen. If liquid was separated in two phases, the Cu in metal liquid can form metallic Ag-Cu eutectic phase. It was shown that the metal liquid wetted all interfaces. So microstructure inhomogeneity was introduced in all sample depending on different liquid composition. In addition, the nucleation and growth of $Bi_2Sr_2CaCu_2O_X$ superconducting phase has been investigated. Superconducting phase was nucleated at $(Sr_{1-X},Ca_X)_{14}Cu_{24}O_X$ phase with orientation relationship. The Ag-Cu eutectic phase and the metallic liquid phase enhanced the growth of Bi-free phase and superconducting phase and caused sausaging effect. In part III, the growth behavior of superconducting and second phases has been studied using a spray drying and ball milled powder. Regardless of powder type, main second phase was changed from $(Sr_{1-X},Ca_X)_{14}Cu_{24}O_X$ to $(Sr_{1-X},Ca_X)_2Cu_1O_X$ with increasing heat treatment time. Superconducting phases $(Bi_2Sr_2CaCu_2O_X$ and $Bi_2Sr_2Ca_2Cu_3O_X)$ grew near the $(Sr_{1-X},Ca_X)_{14}Cu_{24}O_X$ at initial stage of heat treatment. Firstly, $Bi_2Sr_2CaCu_2O_X$ phase grew to penetrate $(Sr_{1-X},Ca_X)_{14}Cu_{24}O_X$ phase. $Bi_2Sr_2Ca_2Cu_3O_X$ phase, then, grew by consumption of $(Sr_{1-X},Ca_X)_{14}Cu_{24}O_X$ and $Bi_2Sr_2CaCu_2O_X$ phase. Even at early sintering stage of 5 hours, 2223 phases were formed near Bi-free phase, while not formed at the place far from Bi-free phase.

서지기타정보

서지기타정보
청구기호 {DMS 97017
형태사항 iv, 138 p. : 삽도 ; 26 cm
언어 한국어
일반주기 저자명의 영문표기 : Dong-Chan Shin
지도교수의 한글표기 : 윤덕용
지도교수의 영문표기 : Duk-Yong Yoon
학위논문 학위논문(박사) - 한국과학기술원 : 재료공학과,
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