PARAMAGNETIC CU2-6.6 PROBED BY EPR AND MAGNETIC-SUSCEPTIBILITY( CENTERS IN OXYCARBONATE PHASE YBA2CU2.95(CO3)(0.35)O)

Room temperature EPR and magnetic susceptibility studies are reported for the YBa2Cu2.95(CO3)(0.35)O-6.6 phase, an intermediate phase in the synthesis of YBa2Cu3O7-delta by a sol-gel route. EPR measurements hav e revealed spectra of Cu2+ ions in an orthorhombic local-crystal symme try which are attributed to copper ions in a modified Cu(1) site. The presence of CO32- groups in the structure, surrounding the Cu(1) atoms , is at the origin of the EPR signal. The values of the g-tensor for t his signal are as follows: g(x) = 2.045(5), g(y) = 2.117(5) and g(z) = 2.228(5). The d.c. magnetic susceptibility has shown a paramagnetic t erm superimposed on the diamagnetic contribution of the superconductin g regions. The temperature dependence of the paramagnetic response is described by a perfect Curie law plus a constant term. The molar Curie constant is 1.1 x 10(-2) cm(3) K/mol Cu. The free spin concentration calculated from this Curie constant agrees well with the intensity of the EPR signal, suggesting it emanates from isolated Cu(2+)paramagneti c centers. (C) 1997 Elsevier Science Ltd. All rights reserved.