NONLINEAR AC SUSCEPTIBILITY AND CRITICAL-CURRENT OF (Y1-XPRX)BA2CU3O7-DELTA CERAMICS

The intergranular critical current density j(cJ)(T) of (Y1-xPrx)Ba2Cu3 O7-delta ceramic samples was determined at zero DC magnetic field by t emperature-dependent AC susceptibility measurements (chi)(T) with diff erent field amplitudes h(AC) as well as by isothermal low-field AC sus ceptibility measurements (chi)(h(AC)) (140 mG less than or equal to h( AC) less than or equal to 18.4 G). In the ''low'' temperature regime, the temperature dependence of j(cJ) was deduced from the initial slope of isothermal (chi)'(h(AC)) measurements. The shift of the intergrain peak in ('')(chi)(T) to lower temperatures with increasing field ampl itude h(AC) was used to determine the temperature dependence of j(cJ) in the ''high'' temperature regime which could be fitted to a power-la w behaviour j(cJ)(T) alpha (1 - T/T-cJ)(beta) with beta approximate to 1. This temperature dependence of the intergranular critical current density j(cJ) indicates that the superconducting grains are connected by insulating interfaces (network of SIS junctions). j(cJ) was found t o decrease monotonically with increasing Pr content x.