Investigation of intra- and intergranular coupling of ferroelectric-superconducting composites ?

We investigated the coupling of specific ferroelectric-superconducting composites with variable volume fraction, particularly because they have presented a superconducting transition at 85 K. The intra- and intergranular coupling of these composites has been considered from the resistivity and susceptibility measurements. Our results show that the transport properties of this kind of composite are governed by different mechanisms, depending on the volume fraction of the ferroelectric material, . Up to intragranular coupling exists between the YBCO superconducting grains, but when the electrical transport is greatly related to intergranular coupling. In this case, two distinct and superconducting phases are evidenced by the susceptibility measurements; they maintain the superconducting character of the composites. Moreover, at the superconducting percolation threshold, the electrical response exhibits some hysteresis giving evidence that internal polarization is important and can play a role in the composite properties.