ORDERING OF OXYGEN IN HALOGEN TREATED 1-2-3-SYSTEMS AS STUDIED BY NQR

We have investigated the low-temperature behavior of Cu NQR for iodina ted RBa2Cu3Ox (R = Y, Gd) compounds. The different influence of Gd spi ns on the Cu(1) and Cu(2) sites was used to separate the contributions of both sites in the spectra. The distinct NQR lines associated with the different oxygen-coordinated Cu(1) sites have been observed. The N QR spectra of the Cu(1) sites show that the iodine treatment gives ris e to the modifications of the oxygen sublattice. From the analysis of the NQR spectra of the Cu(1) sites follows an increase of the average length of the Cu(1)-O chains at treatment.