EPR and magnetic susceptibility investigations of some vanadate–lithium–borate glasses

Abstract

The EPR and magnetic susceptibility data for xV 2O 5(1− x)[2B 2O 3·Li 2O] glasses indicate the presence of both V 4+ and V 5+ valence states. The magnetic susceptibility investigation shows that only a small fraction of vanadium ions are in the V 4+ state and the N V 4+ / N V 5+ ratio decreases when V 2O 5 content increases. The EPR spectra recorded from samples with low V 2O 5 content ( x≤5 mol%) show a well resolved hyperfine structure typical for isolated vanadyl ions in a ligand field of near octahedral ( O h ) symmetry. For x>20 mol% the EPR spectra may be considered a superposition of two signals: one with a resolved hyperfine structure typical for isolated VO 2+ ions in a C 4v symmetry, and the other a broad line without structure, at g≈1.96, assigned to associated vanadium ions. The clustered ions are formed due to the dipole–dipole interactions between V 4+ ions and their number increases with V 2O 5 content. At higher concentrations ( x>20 mol%), V 2O 5 behaves as glass network former together with B 2O 3.