LOCAL CU AND BR ENVIRONMENTS AND THEIR RELATIONSHIP TO SUPERCONDUCTIVITY RESTORATION IN BROMINATED YBA2CU3OY

Cu-63,Cu-65 nuclear quadrupole resonance (NQR) and Br k-edge x-ray abs orption fine structure (XAFS) have been used to study the local struct ures in well-characterized samples of deoxygenated and brominated YBa2 Cu3Oy(YBCO). NQR shows that after bromination of YBa2Cu3O6.1 at 260 de grees C, oxygen has repopulated the chain sites. From XAFS, it is conc luded that Br does not enter the YBCO lattice, but rather precipitates out as small nanoscale particles of BaBr2. These results provide clea r evidence of the role of Br in reoxygenating the YBCO structure and a n explanation for the partial restoration of superconductivity in the YBCO system. (C) 1998 American Institute of Physics. [S0003-6951(98)04 834-7]