INVESTIGATION OF INTRA-GRANULAR AND INTERGRANULAR COUPLING OF FERROELECTRIC-SUPERCONDUCTING COMPOSITES PB2SCTAO6-YBA2CU3O7-DELTA

We investigated the coupling of specific ferroelectric-superconducting composites with variable volume fraction, particularly because they h ave presented a superconducting transition at 85 K. The intra- and int ergranular coupling of these composites has been considered from the r esistivity and susceptibility measurements. Our results show that the transport properties of this kind of composite are governed by differe nt mechanisms, depending on the volume fraction of the ferroelectric m aterial, Phi(PST) UP to Phi(PST) = 0.23 intragranular coupling exists between the YBCO superconducting grains, but when 0.23 < Phi(PST) < 0. 58 the electrical transport is greatly related to intergranular coupli ng. In this case, two distinct and superconducting phases are evidence d by the susceptibility measurements; they maintain the superconductin g character of the composites. Moreover, at the superconducting percol ation threshold, the electrical response exhibits some hysteresis givi ng evidence that internal polarization is important and can play a rol e in the composite properties.