AC CHARACTERIZATION OF PYROSOL AND CVD MADE HIGH-TC MATERIALS

A.c. characterizations have been used to determine the resistivity: ρac, susceptibility: χac and the critical current density: Jc(T) of superconducting thin layers in relation to their preparation conditions. The critical current has been estimated from a very simple contactless technique based on the screening effect due to the superconducting layer when inserted between the primary excitation winding and a secondary pick-up coil. The voltage appearing on the pick-up coil indicates when the magnetic flux penetrates through the layer, that means when the critical current is exceeded in the superconducting state. The high Tc superconductors analyzed have been obtained by two different techniques. The first one is based on the pyrolysis of an ultrasonically deposited gel containing the Y-Ba-Cu precursors, (for R = 0, Tc = 80K on MgO substrates) and the mean critical current density is 4000 A/cm2 at 30K. The other one is a low pressure, low temperature Chemical Vapor Deposition process of Y, Ba and Cu metal complexes (for R = 0, Tc = 89K on SrTiO3 substrates); Jc(T) in that case is much higher: jc = 105 A/cm2 at 77K approaching the values of single cristalline materials. © 1990.