The local structure and interactions between V4+ ions in soda-phosphate glasses

EPR investigation on xV₂O₅ · (100 −x)2P₂O₅ · Na₂O] and xV₂O₅ · (100 −x)P₂O₅ · mNa₂O] (m = 1.5 and 2) glass systems was performed. The changes observed in the EPR spectra of xV₂O₅× (100 −x)2P₂O₅ · Na₂O] glasses with increasing content of vanadium oxide are explained supposing that these spectra consist of two superposed EPR signals, one with hyperfine structure typical for isolated ions and another one consisting of a broad line without hyperfine structure characteristic for clustered ions. The clustered V⁴⁺ ions are not evidenced at low V₂O₅ contents (x = 5 mol%). The EPR spectra of xV₂O₅ · (100 −x)P₂O₅ · mNa₂O] glasses indicate a superposition of two or three hyperfine structures attributed to nonequivalent VO²⁺ centers. Spin Hamiltonian parameters (g, A), dipolar hyperfine coupling parameter (P) and Fermi contact interaction term (K) have been evaluated. The ratio between the number of clustered and isolated ions was also determined.