EPR and magnetic susceptibility studies on V2 O5-P2O5-PbO glasses

EPR and magnetic susceptibility investigations on the glass system with 050 mol % were performed. The covalence degree of vanadium bonds was evaluated according to the LC AO-MO model. The changes observed in the EPR spectra with increasing V⁴⁺ ion content are explained using a simulation program on the assumption of the superposition of two signals, one with hyperfine structure (hfs) typical for isolated ions and another one consisting of a broad line without hfs characteristic for clustered ions. The hfs is not shown for x<3mol%V₂O₅. The EPR data show the presence of V₄₊ ions in a square-pyramidal co-ordination (C_4V) for 3x20mol%V₂O₅. The progressive disappearance of hfs for high V²O⁵ content (>20 mol %) suggests the increase of the associated ion number coupled by superexchange interactions. This result is consistent with magnetic susceptibility data for >3 mol % where the temperature dependence of magnetic susceptibility is described by the Curie–Weiss type law with a negative paramagnetic Curie temperature. The magnetic susceptibility results allowed the estimation of the V⁴⁺/V⁴⁺ + V⁵⁺ ratio in the sample studied.