Electron paramagnetic resonance of Cu 2+ and V 4+ ions in borate glasses

Abstract

The EPR spectra of Cu 2+ and V 4+ ions have been studied in binary ROB 2O 3 glasses (where R = Ba, Sr, Pb and Zn) and in ternary PbOZnOB 2O 3 glasses. The main results of an EPR study of alkali-borate glasses are briefly reviewed. Three distinct EPR spectra of Cu 2+ ions in barium-borate glasses were observed. The superposition of two EPR spectra of a Cu 2+ ion in glasses containing from 5 to 15 mol.% BaO is attributed to a stable liquid immiscibility in these glasses. The structural similarity of barium- and strontium-borate glasses containing 30–40 mol.% RO is established. It is concluded that non-bridging oxygens appear in these glasses for higher concentrations of a modifier than in alkali-borate glasses. The data for Cu 2+ ions in PbOB 2O 3 glasses containing from 20 to 40 mol.% PbO suggest a modifying role for Pb 2+ at such PbO concentrations. Very marked differences between the spectral parameters of low- and high-lead borate glasses are found for a V 4+ ion. The superposition of two distinct EPR spectra of V 4+ ions in binary ZnOB 2O 3 glasses is observed and is attributed to the two-phase structure of these glasses. The structural roles of Pb 2+ and Zn 2+ in ternary PbOZnOB 2O 3 glasses are discussed. The tendency of the Cu 2+ ion to be localized far from lead and zinc ions playing the roles of network formers is established. The high sensitivity of the V 4+ EPR spectra to the main structural units is suggested.