Screening properties and critical current of superconductor-MgO composites

A series of composites of the high temperature superconducting (HTSC) phase (Bi,Pb)(2)Sr2Ca2Cu3Ox (2223) with MgO were prepared. AC susceptibility mea surements showed a percolation effect in the screening properties and criti cal current around 50 vol.% superconducting material, while maximum screeni ng is reached at 70 vol.% of the HTSC phase. The shielding efficiency of su perconducting material added to the composite is highest in the composition range between 40 and 70 volume percent HTSC phase. this behaviour can be u nderstood in terms of random distribution of superconducting and non-superc onducting phases and the occurrence of intergrain coupling effects. (C) 199 9 Elsevier Science Ltd. All rights reserved.