Electron Spin Resonance Spectra of Gamma-Ray-Irradiated Phosphate Glasses and Compounds: Oxygen Vacancies

Abstract

The electron spin resonance spectra of γ-ray-irradiated glassy and polycrystalline phosphorus pentoxide and alkali phosphates with molar ratios of phosphorus pentoxide to alkali oxide ranging from 3.33 to 0.625 have been observed at 10 and 35 Gcps and at 300° and 78°K. Well-resolved hyperfine doublets were observed in each glass or polycrystalline powder. Additional resonances were also present in all the specimens but these are not discussed. The widths and shapes of the doublets were independent of temperature and only small alterations in the shapes of each component of a doublet were found as a function of frequency. One set of doublets has been discussed elsewhere and is not considered. Those doublets which are discussed are attributed to an electron trapped at a nonbridging oxygen vacancy. Interaction of the electron with the nearest-neighbor 31P nucleus (100% natural abundance, I = 12) produces the doublet structure. These doublets exhibited isotropic hyperfine interactions ranging from 1880 to 4490 Mcps. The smaller interactions, 1880-2196 Mcps, were found in glasses and polycrystalline powders with molar ratios ≤ 1 and the larger interactions, 2630-4490 Mcps, were found in those with molar ratios > 1. The anisotropic hyperfine interaction, (A‖ − A⊥) / h, of all the doublets was ≤ 540 Mcps. The defect electron state is assumed to be the nonbonding phosphorus sp hybrid orbital. On the basis of this assumption, the different isotropic hyperfine interactions are attributed to different geometric configurations of the phosphorus ion and the oxygens to which it is bonded. The assumed sp hybridization accounts for most of the electron density. An approximate g value is calculated for the doublets and is found to range from 2.005 to 2.040.