Enhanced inter-plane coupling of Mg doped Cu0.5Tl0.5Ba2Ca2−xMgxCu3O10−δ superconductors: XPS and FTIR studies

A comparison of X-ray photoemission spectroscopy of Mg doped Cu0.5Tl0.5Ba2Ca1.5Mg0.5Cu3O10−δ and Mg free Cu0.5Tl0.5Ba2Ca2Cu3O10−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 Cu0.5Tl0.5Ba2O4−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 Cu0.5Tl0.5Ba2(Ca0.5Mg1.5)Cu3O10−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 kF, ξc, VF, and hence the superconductivity parameters.