EPR investigations of superconducting metaloxide ceramics

EPR (3 cm) of metaloxide ceramics La2CuO4, La1.8Sr0.2CuO4-y, Y1.2Ba0.8CuO4-y, Y1Ba2Cu3O9-y is investigated at 4.2 < T < 300 K. It is shown that spin paramagnetism of Cu in the first two compounds is strongly depressed. The EPR signal intensities correspond to only several percent of Cu in the uncompensated spin Cu2+ state. In the two latter ceramics strong EPR signals of Cu2+ are observed, but they relate to the phase which is not responsible for superconductivity and are insensitive to Tc. The obtained results may indicate that the main part of Cu ions are in spinless Cu+ states of in the states of higher valence, ordered antiferromagnetically with TN > 300 K