T1(Ba,Sr)2Ca2Cu3Ox高溫超體離子缺陷，取代化學與超導性之研究

Abstract

本研究的主要目的在於探討離子缺陷，離子取代對高溫超導相 Tl (Sr,Ba)2Ca2Cu3O2(Tl-1223) 的結構、超導性、磁性和微結構所造成的影響。我們改變鍶以及鉛離子來研究Tl(Sr, Ba)2Ca2Cu3O2相的形成。並以ICP-MS來定量(Tl, M)(Sr, Ba)2Ca2Cu3O2的計量與組成，更深入的了解化學計量對結構與超導性所扮演的角色。我們所得到的主要結果如以下所示： (a) Tl(Sr2-xBax)Ca2Cu3O2只有在0.5<x<0.8的範圍，可以得到穩定的結構，並且他的最高臨界溫度存在於TI(Sr1.2Ba0.8)Ca2Cu3O2相，而再現性比較好的Tl(Sr1.5Ba0.5)Ca2Cu3O2相臨界溫度就比較低。 (b)就 (TI, M)(Sr1.5Ba0.5)Ca2Cu3Ox的取代而言，鉈缺陷與氧缺陷會隨著取代離子種類而變化。當M＝ln, Pb和Bi的時候，缺陷會隨著取代量增加而減少，但當M＝K時，則會隨著取代量增加而增加。儘管有很大的鉈缺陷 (可以高達60%)，但是通常都還是可以維持著結構的穩定性。 (c) Tl(Sr1.5Ba0.5)Ca2Cu3Ox的氧缺陷濃度 (80%) 非常高。除非以元素取代的方式可以增加氧含量之外，其他例如增加退火時間，以高壓氧氣退火的方式，都無法有效的增加氧含量 (x<8.75)。 (d) Tl(Sr1.5Ba0.5)Ca2Cu3Ox若我們以鉛或是鉍取代鉈，則可以減少氧的缺陷。在增加氧含量的過程中，我們計算得到每增加一個鉛或鉍離子的取代，可以增加2.86及8.4l個氧原子。而這個範圍是在鉛取代量等於0<X<0.2之間，鉍取代量0<x<0.05之間。 (e) 不同金屬離子 (Tl1-xMx)(Sr1.5Ba0.5)Ca2Cu3Ox對鉈的取代極限分別是鉛0.6、鉍0.25、鉀0.25與銦0.25。其中當取代離子為鉛以及鉍時、臨界溫度會隨著取代量增加而增加。而當取代離子為鉀或銦時，臨界溫度則不會隨著取代濃度變化。 (f) 在 (Tl1-xMx)(Sr1.5Ba0.5)Ca2Cu3Ox (M=Pb, Bi, In and K) 中，就SEM以及AFM所觀察到的晶粒特性，發現鉍、鉛、銦對樣品的結晶性都有幫助，只有鉀會產生晶界對結晶性造成不好的影響。因此我們認為鉍、鉛、銦容易在晶粒內造成雜質，而鉀則是在造成晶界的雜質。

This research is attempted to investigate the effect of ion defects, ion substitution and dopant contents on the crystal structure, superconductivity, magnetic properties, and microstructure of high-T, Tl(Sr, Ba)2Ca2Cu3O2 (Tl-1223) phases. A variety of attempts including doping of Sr and Pb ions have been made in order to study the formation of pure Tl(sr, Ba)2Ca2Cu3O2 phases. Furthermore, in order to understand the role that chemical composition plays we have determined the composition of constituent ions by ICP-MS analysis and study the crystal structure and superconductivity of M-doped (Tl,M)(Sr, Ba)2Ca2Cu3Ox (M＝Pb, Bi) samples. Major results of this research are summarized in the followings. (a) The structural stability for Tl(Sr2-xBax)Ca2Cu3O2 phases has been determined to be in the range of 0.5 < x < 0.8 and the optimal Tc was found in the poorly reproducible Tl(Sr1.2Ba0.8)Ca2Cu3O2 phase, whereas lower Tc was found in the highly reproducible Tl (Sr1.5Ba0.5)Ca2Cu3O2 phase. (b) The deficiency of Tl3+ and oxygen composition of M-doped Tl(Sr, Ba)2Ca2Cu3O2 phases was found to be dependent on the dopant contents. The Tl deficiency was found to decrease with increasing M content for phases with M＝In, Pb and Bi, whereas that was found to increase for the sample with M＝K. In spite of large Tl deficiency (i.e., in some cases it can be as large as 60%) in the crystal lattice Tl-1223 still exhibits high structural stability. (c) On the other hand, the degree of oxygen deficiency in the Tl(Sr1.5Ba0.5)Ca2Cu3O2 phases was found to be fairly large (i.e., as large as 80% in some cases). Unless metal ion-doping is carried out in the Tl-1223 phase, processing conditions such as prolonged or high-pressure annealing attempted to increase oxygen content of the Tl-1223 samples were found to be ineffective and the maximal value of z could only reach 8.75 without M doping. (d) The oxygen deficiency of (Tl1-xMx)(Sr1.5Ba0.5)J)Ca2Cu3 phases can be effectively reduced when Tl3+ is substituted by cations of Pb or Bi. We have also estimated the increment of oxygen composition (i.e., hole doping) to be 2.86 and 8.41 per M atom upon doping for phases with M＝Pb (0 < x < 0.2) and Bi (0 < x < 0.05), respectively. (e) The substitution limit of M for Tl in (Tl1-xMx)( Sr1.5Ba0.5) Ca2Cu3O2 has been determined to be 0.6, 0.25, 0.25 and 0.25 for phases with M＝Pb, Bi, K and In, respectively. Tc of M-doped Tl- 1223 phase was found to increase with increasing M content for phases with M＝Pb, Bi, while that of K- or In-doped Tl-1223 phases was found to be unchanged with increasing dopant content. (f) Pb-, Bi-, In- and K-doping in the (Tl1-xMx)(Sr1.5Ba0.5) Ca2Cu3O2 phases will result in formation of impurities which may be related to the pinning of M-doped Tl-1223 phases. Furthermore, we propos that intragrain impurities were likely to form in samples doped with Bi, Pb and In while intergrain impurities were found to exist in K-doped Tl-1223 phase, as indicated by x-ray diffraction, SEM, and AFM measurements.