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研究生:余宏達
研究生(外文):Yu,Hong-Da
論文名稱:高溫超導YBa2Cu4O8/Ag複合材料之合成與分解程序
論文名稱(外文):book
指導教授:吳乃立
指導教授(外文):Wu,Nae-Lih
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:化學工程研究所
學門:工程學門
學類:化學工程學類
論文種類:學術論文
論文出版年:1993
畢業學年度:81
語文別:中文
論文頁數:111
中文關鍵詞:高溫超導體複合材料合成程序分解程序臨界電流密度
外文關鍵詞:high-Tc superconductorcompositeSynthesis process
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在YBa2Cu4O8(124化合物)相穩定區域內(溫度:810-880C,氧壓:1
-50atm),利用電子顯微鏡(SEM)、能量散佈X-光分析儀(EDX)、X-光繞射定
量分析(XRD)及臨界溫度(Tc)的測量,調查銀對於YBa2Cu3O7-x(123化合物)
與YBa2Cu4O8之間的相轉(合成反應:123+CuO-->124,分解反應:123
-->124+Y-Ba-Cu-Oxide)所產生的效應。我們發現銀皆可加速此二反應的
進行。尤其,當銀在高氧壓下熔融時,相轉換的速率更是快速地增加。這些
結果顯示,液態的銀其加速效應較固態的銀更為顯著,這是因為液態的銀提
供一個較佳的擴散途徑。銀加速了合成反應,124為唯一產物。而分解反應
中的速率較合成反應為慢,且除了124之外尚有Y2BaCuO5及Ba-Cu- Oxide等
副產物產生。EDX分析顯示在這兩個反應中,銀並不會進入124晶粒中。而
銀填充於晶粒之間,使得樣品結構緻密。以合成反應及分解反應所製得
之124-Ag複合塊材,其臨界溫度(Tc)分別為78-80K及75-80K。利
用124-->123+CuO之分解反應,其中微細的CuO在樣品中可以產生釘紮中心(
pinning center),進而改善超導體的晶粒內及晶粒間電流密度。本研究
中,我們選擇了兩個分解程序,一為高溫程序(900C,空氣中),另一為高溫程
序(700C,2.5torr氧壓)。不同的分解時間,其晶粒內臨界電流密度及晶粒
間臨界電流密度皆同時被調查。在高溫程序中,CuO快速擴散至晶界,因晶
界中有Ag的存在,而使晶界發生部份熔融現像阻礙晶粒的連接,進而影響電
流的傳遞,使得晶粒內的Jc可提高,但晶粒間的Jc卻減小。相反的,在低溫
程序中,分解速率及CuO的擴散速率皆相當緩慢,容易產生有效的釘紮中心,
亦不會有部份熔融現像發生,晶粒內及晶粒間的Jc皆可提高,在分解時間小
於5小時內,晶粒間的Jc皆大於原始124。尤其,分解1小時後,具有最大晶粒
間的Jc。

The effects of silver on the phase transformation from YBa2Cu3
O7-x(the 123 compound) to YBa2Cu4O8(the 124 compound) via
either the synthesis reaction (123+CuO-->124) or the
decomposition reaction (123-->124+Y-Ba-Cu-Oxide) were
investigated, by using SEM,EDX,XRD,and Tc measurements, under
the conditions(temperature:810-880C, oxygen pressure:1-50atm)
where 124 is the thermodynamically stable phase. It was found
that both reactions were greatly accelerated by silver. In
particular, the tranformation rates increase tremendously when
silver melts at high oxygen pressure. These results suggest
that liquid Ag is more effective than solid one in accelerating
the reactions. This is attributed to the better diffusion
environment supplied by liquid Ag. 124 is the sole product of
the Ag-accelerated synthesis reaction. The decomposition
reaction, which is slower than synthesis one, produces not only
124 but also the by-products including Y2BaCuO5 and Ba-Cu-Oxide
. EDX analysis indicated no Ag within 124 grains resulting
from both reactions. The prepared 124-Ag composites have a
dense structure with Ag filling in the voids between the
neighnoring oxide grains, and the superconducting critical
temperatures are 78-80K and 75-80K for those prepared by the
synthesis and decomposition reactions, respectively. We have
also attempted to improve the critical current densities(Jc) of
YBCO/Ag composites, via 124 decomposition reaction
(124-->123+CuO). In this study, two different sets of
decomposition conditions were carried out, including a high-
temperauter process (HT: 900C, in air) and a low-temperature
one (LT: 700C, 2.5torroxygen pressure). The inter-grain and
intra-grain Jcs were measured as a function of decomposition
times. For the HT process, partial-melting at grain boundary
occurs, due to the coexisting of 123, CuO and Ag, and it
deteriorates the link between grains, and reduces the transport
current. As a results, while intra-grain Jc can be increased

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