INSULATING-(SUPER)CONDUCTING TRANSITIONS IN NEW FERROELECTRIC-SUPERCONDUCTOR COMPOSITES - PB92(SCTA)O-6-YBA2CU3O7-DELTA

We studied the structural and electrical properties of ferroelectric-s uperconductor composites with variable volume fractions. Specifically, the insulating-(super)conducting transition is examined. Our results show that compatibility between Pb-2(ScTa)O-6 ferroelectric and YBa2Cu 3O7-delta superconducting materials is strong, as superconducting comp osites with 56% of ferroelectric material in volume have a zero resist ance critical temperature at 87 K. From resistivity measurements, the critical fraction of YBCO, for which the insulating-superconducting tr ansition occurs at low temperature, and the percolation threshold for the insulating-conducting transition at room temperature are evaluated , For this second transition, we estimate that the transport critical exponent, t=2.0+/-0.3, is in excellent agreement with the percolation theory in three dimensions (3D). This gives strong evidence that trans port in the composites takes place in 3D and indirectly confirms that the interfacial reactivity between the two materials is very weak, as shown by the X-ray diffraction patterns, (C) 1997 Elsevier Science B.V .