EPR study of molybdenum-lead-phosphate glasses

The local symmetry and interaction between paramagnetic ions in xMoO3(1 − x)[2 P2O5PbO] glasses with 0.5 ⩽ x ⩽ 50 mol% are investigated by EPR spectroscopy. For x ⩽ 10 mol% the isolated Mo5+ ions surrounded by five oxygen ligands in a square-pyramidal form (C4v symmetry) prevail. The short range disorder in the environment of Mo5+ ions is not significantly (ΔR/R ≈ 2%). At high molybdenum content (x > 20 mol%) the dipole–dipole and superexchange coupled Mo5+ ions appear and their number increases with the MoO3 content. These two aspects are also correlated with the network modifier and former role of molybdenum oxide in function of its concentration. Thus a strong depolymerization of the phosphate structure and the formation of P–O–Mo or Mo–O–Mo bonds in studied glasses appear.