PLASMA-ENHANCED FLUORINATION OF YBA2CU3O7-DELTA CERAMICS .2. INTERACTION MECHANISMS BETWEEN THE REACTIVE SPECIES AND THE MATERIALS

Mechanisms of interaction between the reactive species of a (CF4 + 02) plasma and YBa2Cu3O7-delta ceramics have been proposed through detailed angle-resolved X-ray photoelectron spectroscopic analyses. At the surface of the outer grains, the plasma treatment removes (OH)- and (CO3)2- species contained in the degradation layer and gives rise to a fluoride-rich layer, whereas in the bulk of the material the occurrence of metal-fluorine bonds in the superconducting phase has been assumed. An increase of the oxidation state of copper has been also detected, confirming the oxidizing effect of the plasma treatment. A comparison with the oxidation mechanisms obtained by fluorine gas treatment is proposed.