Abstract:
The effect of disorder on the suppression of superconductivity has been studied in two series of high temperature superconducting oxides of the type Ln1.2Ba1.2Ca0.6Cu3O7+δ (Ln = La, Nd, Sm) and La1.2−xNdxBa1.2Ca0.6Cu3O7+δ (x = 0.3, 0.6, 0.9). These oxides crystallize in the tetragonal structure related to the 1113-type superconductors. It has been shown that considerable cation disorder exists at the Ln and Ba crystallographic sites in these oxides. Furthermore, it has been shown that Ln and Ca ions occupy both the 1d- and the 2h-crystallographic sites whereas Ba ions only occupy the 2h-crystallographic site. La1.2Ba1.2Ca0.6Cu3O7+δ shows a superconducting transition with Tc of 65 K while the Sm analog shows semiconducting behavior. A broad metal–semiconductor transition is observed in Nd1.2Ba1.2Ca0.6Cu3O7+δ. It has also been shown that the gradual suppression of Tc in La1.2−xNdxBa1.2Ca0.6Cu3O7+δ, as x increases, is related to disorder which could be related to the variance (σ2) of the average ionic radii of the ions at the 2h site.