The effect of rare earth oxide substitution on the magnetic properties of Tl-based superconductors

The effects of the heterovalent substitution of the rare earth ions La 3+, Sm 3+, Pr 3+, Dy 3+ and of Y 3+ into the Ca 2+ separating layers on the magnetic properties of (Tl,Pb)-1223 and (Tl,Pb)-1212 superconductors are reported. Nominal compositions of (Tl 0.6Pb 0.5)(Sr 0.8Ba 0.2) 2(Ca 1− x M x ) 2Cu 3O 8+ δ , where M=La, Sm, Pr, Dy, Y and x=0.0, 0.05, 0.1, 0.15 and 0.2 were investigated. Increasing contents of the rare earth elements enlarged the superconducting Tl-1212 phase in the samples. This led to a decrease of the T c values. AC and virgin volume magnetization characteristics of all fabricated samples were measured at 77.3 K in magnetic fields ranging from 10 −1 to 10 5 Am −1. A decrease in the content of the Tl-1223 phase affected the magnetization mainly in the range of stronger fields around 10 5 Am −1. For the lower substitution levels ( x=0.05, 0.1) an improvement of the intergrain links was found.