An electron paramagnetic resonance study of Y-Ba-Cu-O-type ceramics in superconducting and nonsuperconducting phases

Abstract

Electron paramagnetic resonance (EPR) studies of high-temperature superconducting and nonsuperconducting Y-Ba-Cu-O compounds were performed. The effect of different oxygen treatments on the EPR spectra was analysed. Changes were found in the linewidth and in the signal intensity. The compound in the so-called 'green phase' gives rise to a very symmetric EPR line, in contrast with the highly asymmetric lineshape arising from the superconducting samples. The signal, with g approximately=2, is attributed to Cu2+ ions in sites with axial and lower symmetry. A possible correlation with the Jahn-Teller effect is suggested. EPR spectra from iron-substituted samples provide further information about the local environment of Cu(I) sites.