EPR STUDY OF LOCALIZED CU2+ PARAMAGNETIC-IONS AND CU2+ PAIRS IN THE OXYGEN-DEFICIENT PRBA2CU3O6+X AND PR(0.5)R(0.5)BA(2)CU(3)O(6+X) (R=Y,ER) COMPOUNDS

Low-temperature EPR measurements are presented for the PrBa2Cu3O6+x and Pr(0.5)R(0.5)Ba(2)Cu(3)O(6+x) (R = Y,Er) compounds with oxygen deficiency (tetragonal phase). The nuclear hyperfine interaction of the Cu2+ ions has been observed in both compounds. The origin of the Cu2+ EPR spectra has been associated with localized divalent copper ions in the Cu(1) sites. A time-induced transformation of the Cu2+ local crystal-held symmetry from orthorhombic to tetragonal, related to the oxygen distribution in the Cu(1) plane, has been detected. The EPR spectra of pairs of weakly exchange-coupled divalent copper ions were also observed. These copper pairs are suggested to occur in the Cu(1) planes and to be magnetically isolated from the antiferromagnetic CuO2 planes.