PASSIVATION PROCESS OF HIGH T_{<font>c</font>} SUPERCONDUCTORS <font>YBa</font>₂<font>Cu</font>₃<font>O</font>_7−δ BY FLUORINE GAS TREATMENT

Abstract

The atmospheric degradation of high T c superconductors YBa 2 Cu 3 O 7−δ can be prevented using fluorine gas processings around room temperature. A thin layer of amorphous fluorides (and/or oxyfluorides) is formed at the surface of the particles, which passivates the material against hydrolysis and gas-exchange processes. A fluorination mechanism has been proposed, which can account for both fluorine analysis and weight uptake. The superconductivity onset does not seem to be affected by fluorination. Furthermore, an improvement of the shielding effect-Meissner effect cycle to 91% reversibility is achieved when F 2 -treated oxides are heated at 350°C under vacuum.