Critical current density and magnetic behaviour of superconducting YBa<SUB>2</SUB>Cu<SUB>3+y</SUB>O<SUB>7-delta</SUB> : Ag<SUB>x</SUB> composite

The effects of silver additive on the superconducting properties of YBa2Cu3+yO7- delta : Agx for x=0.1, 0.3, 0.6 and 1.2 are studied by measuring the real and imaginary components of the magnetic response in an AC field. The data are fitted to Bean's critical state model and are used to obtain the macroscopic critical current density. The magnetic susceptibility and critical current density are found to depend on the silver content whereas Tc remains essentially unchanged. For x=1.2 the critical current density sharply increases below 77 K. The results suggest that the silver improves the properties of grain boundaries and enhances the intergranular coupling. The real part of the magnetic response is found to be a function of Ha/H∗, where H∗ is the value of the field when the critical-state profile reaches the centre of the specimen