Enhanced inter-plane coupling of Mg doped Cu_0.5Tl_0.5Ba₂Ca_2−xMg_xCu₃O_10−δ superconductors: XPS and FTIR studies

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• 作者：A.A. Khurram ; Nawazish A. Khan ; M.M. Ahadian ; Azam Iraji-zad
• 关键词：Cu_0.5Tl_0.5Ba₂Ca_2-xMg_xCu₃O₁₀₋ ; _δ ; superconductor ; Low anisotropy ; X-ray photoemission spectroscopy
• 刊名：Physica C
• 出版年：2008
• 期刊代码：80_09214534
• 类别：ms
• 出版时间：1 March 2008
• 卷：468
• 期：5
• 页码：405-410
• 文件大小：900 K

摘要

A comparison of X-ray photoemission spectroscopy of Mg doped Cu_0.5Tl_0.5Ba₂Ca_1.5Mg_0.5Cu₃O_10−δ and Mg free Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ superconductor samples have been made. The main objective of these studies is to see the effect of Mg doping in developing better inter-plane coupling among the CuO₂ planes and its effects on the chemical shift of the bonding species. Through these studies it is observed that thallium is in Tl⁺¹ oxidation state in the Cu_0.5Tl_0.5Ba₂O_4−δ charge reservoir layer in both Mg doped and Mg free samples, however, the XPS line related to Ba atoms are shifted to higher binding energy side by 0.32 eV in Mg doped sample. This chemical shift is most likely due to presence of Ba atoms in the immediate vicinity of Mg atoms in Cu_0.5Tl_0.5Ba₂(Ca_0.5Mg_1.5)Cu₃O_10−δ samples. Moreover, the binding energy of Cu atoms observed in XPS measurements is significantly shifted in magnesium substituted samples, which has provided an unequivocal evidence of enhanced inter-plane coupling. The enhanced inter-plane coupling promotes the enhancement of k_F, ξ_c, V_F, and hence the superconductivity parameters.