PLASMA-ENHANCED FLUORINATION OF YBA2CU3O7-DELTA CERAMICS .1. IMPROVEMENT OF THE SUPERCONDUCTING PROPERTIES

The radiofrequency plasma technique involving mixtures of CF4 + O2 gas es has been applied to the surface treatment of high T(c) superconduct ing oxides (YBa2Cu3O7-delta). Investigation of the various experimenta l parameters of the process has shown that the improvement of the crit ical current density, J(c), mainly depends on the inlet precursor comp osition CF4 + tau%02, on the total pressure and on the reaction time. The presence of fluorine in the bulk of the ceramics has been observed from electron microprobe analysis, together with an increase of the ' 'Cu3+'' content. The plasma-enhanced fluorination (PEF) treatment impr oves the superconducting properties of the materials: both values of t he resistivity in the normal state and of the superconducting transiti on width are reduced and the critical transition temperature is improv ed by about 1 K.