Non-isovalent substitution of Ba2+in superconducting YBa2Cu3O7-y

We report the structural, magnetic and superconducting properties of YBa2−xMxCu3O7(M=La3+or K+). Single-phase compounds form over a wide range of x in YBa2−xMxCu3O7and up to x = 0.2 in YBa2−xMxCu3O7. A substituent concentration of 15% triggers an orthorhombic to tetragonal phase15 transition in both systems. In spite of the associated disorder in the Cu(1)-0(1) chains, such a transition does not affect Tcdrastically. Tcgets systematically depressed with increasing x. A temperature-dependent paramagnetic response is observed in YBa2−xMxCu3O7between 90 and 300K.