Processing parameters and kinetics of bromination and chlorination in the YBa/sub 2/Cu/sub 3/O/sub 6+x/ system

The introduction of halogens such as Cl/sub 2/ and Br/sub 2/ can restore 90 K superconductivity to oxygen deficient YBa/sub 2/Cu/sub 3/O/sub 6+x/. This is potentially important for applications to thin-film devices due to the low processing temperatures required relative to reprocessing with oxygen. Low-temperature (260 degrees C) and short-time (>5 min) bromination has been shown to convert initially insulating YBa/sub 2/Cu/sub 3/O/sub 6.2/ powder to a high-temperature superconductor with properties similar to the standard O/sub 7/ material. This process has now been extended to single crystals as well, but with somewhat different processing parameters. Thermal gravimetric analysis (TGA) coupled with mass spectrometry indicated that the Br becomes strongly bonded with no release of Br observed in taking powder samples to 1000 degrees C in flowing forming gas (2%H/sub 2//98%N/sub 2/). The reaction has also been found to be highly exothermic for both Br and Cl treatments, which is consistent with the strong bonding of the bromine.