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 La3+, Sm3+, Pr3+, Dy3+ and of Y3+ into the Ca2+ separating layers on the magnetic properties of (Tl,Pb)-1223 and (Tl,Pb)-1212 superconductors are reported. Nominal compositions of (Tl0.6Pb0.4)(Sr0.8Ba0.2)2(Ca1-xMx)2Cu3O8+d, 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 Tc values. AC and virgin volume magnetization characteristics of all fabricated samples were measured at 77.3 K in magnetic fields ranging from 10-1 - 105 A m-1. A decrease in the content of the Tl-1223 phase affected the magnetization mainly in the range of stronger fields around 105 A m-1. For the lower substitution levels (x = 0.05, 0.1) an improvement of the intergrain links was found.