EPR and magnetic susceptibility studies of Cu2+ ions in TeO2-B2O3-PbO glasses

Results of EPR and magnetic measurements performed on xCuO(1 - x)[70TeO(2) - 25B(2)O(3) - 5PbO] glasses with O < x less than or equal to 40 mol % are reported. The modifications of EPR spectra with the increasing CuO content are explained as the result of the superposition of two EPR absorptions, one showing the hyperfine structure typical for isolated Cu2+ ions and the other consisting of a broad line centered at g congruent to 2.2 typical for clustered Cu2+ ions. Beside the dipole-dipole coupling between Cu2+ ions, the EPR and magnetic data suggested that for x greater than or equal to 20mol %, negative superexchange interactions appear, too. The values of the EPR parameters and magnetic moments prove that the Cu2+ ions are situated in axially distorted octahedral vicinities. From the measured Curie constants it was established that in this glass system for x greater than or equal to 20mol % the copper ions are in Cu2+ and Cu+ valence states. For samples with x greater than or equal to 20 mol %, a downward curvature of the reciprocal susceptibility dependence with temperature was observed at T < 25 K. The magnetic behaviour of CuO-TeO2-B2O3-PbO glasses are analyzed in terms of a random distribution of Cu2+ ions in the glass matrix.