補償塊材組成對含鉛鉈系高溫超導薄膜相形成之影響

Abstract

Tl1Ba2Ca2Cu3O9-δ相(Tl-1223相)因為具有：1.相鄰兩單位晶胞內的銅氧 層間距較短(~8.8A); 以及2.超導臨界溫度高(Tc~115-120K)的優點，故在 應用潛力與超導性質的研究上均引起相當大的注意。但是1223相比起其他 兩種鉈系高溫超導相，Tl-2223相和Tl-2212相，因為成長的條件範圍較為 狹窄，使得製作過程中環境條件的控制較為嚴苛。本實驗在Tl-Ba-Ca-Cu- O系統中用鉛(Pb)取代部份的鉈(Tl)，並改變退火時補償塊材的成份以及 熱處理條件來研究其對Tl-1223相形成之影響。以起始組成計量比接近 於1223的薄膜作為先驅膜，使用計量比為TBCCO-2223的塊材作為熱處理時 的補償，改變不同的氧氣壓力範圍，可以製作出接近純相的Tl-2223及 Tl-2212相薄膜。接著由製作出2223相的條件中，降低基板的溫度，製作 出純相的1212相的薄膜。然後藉著改變補償塊材中鉈的含量，找到了形 成1223相薄膜的條件。由實驗結果可以發現：除了氧氣分壓、基板的溫度 之外，補償塊材的組成成份，似乎是決定薄膜形成的超導相之最重要因數 。 Because of the following two merits: 1. the interlayer distance between two groups of Cu-O trilayers within a unit cell is short (~8.8A) compared to that of Tl-2223 and 2. the higher superconducting critical temperature (Tc ~ 115-120K) compared to that of YBCO. Tl1Ba2Ca2Cu3 O9-δ phase has been considered as a material of high application potential. As a result, it has attracted much attention recently. Nevertheless, the conditions for the forma-tion of the Tl-1223 phase are much more restrictive in comparison to that of the other two high-Tc phases of Tl-based superconductors, 2212 and 2223. In this study, we have tried to extend the formation conditions of Tl-1223 phase by partially substituting Tl with Pb, and by changing the composition of the compensating bulk material.Tl, Pb)-2212 phase were produced in different ranges of O2 gas pressure by using the precursor films with nominal stoichiomentry of Tl:Ba:Ca:Cu = 1:2:2:3 and compensated by bulk material with nominal stoichiomentry of Tl:Ba:Ca:Cu = 2:2:2:3 during annealing. By reducing the anneal temperature under essentially the same conditions, the phase formed in the film became mostly (Tl,Pb)-1212 phase. More interestingly, it was found that the formation of (Tl,Pb)-1223 phase can be realized only by changing the Tl content of the compensating bulks. The results imply that the composition of the compensating bulk may have played a major role in determining the phases formed during post annealing process regardless of the starting composition of the precursor films.