釔鋇銅氧-247 高溫超導體中銅取代之研究

Abstract

本研究利用高溫高壓法合成鋅,鐵,鎳,鋁取代釔鋇銅247相系統, 以了解釔 鋇銅247相中銅原子被其它金屬取代對超導性的影響. 鋅,鎳,鐵,鋁以X光 繞射分析方法得知在組成上的極限溶解度分別為 0.15 , 0.15 0.08和0.06.在所有銅取代釔247相系統中,當取代濃度大於0.03以上時,在 導電性及磁性的量測上均會出現兩相的情況,可見金屬取代釔247系統中的 銅原子,對超導性的影響與金屬本身的磁性,價數及離子半徑大小並無一定 的關係.進一步的特性鑑定包括直流四極探針法,直流磁化率量測電子探針 微區分析(EPMA)及掃描式電子顯微鏡(SEM)分析.根據取代極限溶解度及晶 格常數計算之結果, 我們推論鋅和鎳可能是取代在銅氧平面上,而鐵和鋁 則取代在鏈上的位置. 此外,我們並將本研究的結果與文獻 銅取代釔鋇 銅123及124相系統作一比較. This research is attempted to synthesize several series ofhe copper substituted Y-247 phases by high-pressure method and investigate the effect of metal substitution for copper on the superconductivity of the Y-247 superconductor. The substi-ution limits of metal ions have been determined to be 0.15 , 0.15,0.08 and 0.06 for Zn,Ni,Fe and Al,respectively, based onhe identification of X-ray diffraction patterns. The super- conducting transition substitution(Tc) was found to be signi- ficantly suppressed upon metal substitution regardless of the difference in the magnetic property,valence states and ionic radius of the individual metal ion. Multiphase products have been observed in the metal-doped Y-247 with substitution con- centration greater than 0.03. Further characterizations of metal-doped 247 phases were carried out by employing dclectrical resistivity,dc magnetization,electran probe micro- lysis (EPMA) and scanning electron microscopic (SEM) tech- niques. Based on the substitutional limit and lattice constantseterminations, we have deduced that Zn and Ni are likely totitute the Cu atoms in the copper-oxygen planes, whereas Fe and Al prefer and enter the Cu-sites in the copper- oxygen chain presumably in a random fashion. We have also compared the re- ported results of the similar metal substitution for copper in the corresponding Y-123 and Y-124 analogoues.