XRD EPR STUDIES OF CERAMICS PR0.5RE0.5BA2CU3O7-DELTA IN THE ORTHORHOMBIC AND TETRAGONAL PHASE

EPR, XRD, and magnetic studies are presented for Pr0.5Re0.5Ba2Cu3O7-delta compounds (Re = La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu) in the orthorhombic and tetragonal (large oxygen deficiency) phase. For the samples with Re = Dy, Ho, Y, Er, Tm, Yb, and Lu in the orthorhombic phase, the transition to the superconducting state has been observed in the temperatures range T(c) between 18 and 40 K. For the samples with Nd and Yb in the tetragonal phase, EPR spectra coming from trivalent rare earth ions have been recorded. In the nonoxygenated sample Pr0.5La0.5Ba2Cu3O7-delta the EPR spectrum arising from the non-Kramers trivalent praseodymium ion has been observed. A broad EPR line appearing in all our samples was attributed to superexchange interaction between copper ions over oxygen (O2-) bridges. Interestingly, for the Pr0.5Re0.5Ba2Cu3O7-delta (Re = Er and Lu) compounds in the tetragonal phase at liquid-nitrogen temperature, a nonresonant microwave absorption in low magnetic fields has been detected.