STRUCTURAL CHARACTERISATION OF V2O5 - Bi2O3 - B2O3 SYSTEM 
BY IR ABSORPTION AND EPR

C. Tripon, D. Toloman, O. Cozar1,I. Bratu and I. Ardelean1

National Institute for Research and Development of Isotopic and Molecular Technologies, P.O. Box 700, RO-400293,               Cluj-Napoca, Romania
1 Faculty of Physics, Babes-Bolyai University, RO-400084, Cluj-Napoca, Romania

The structure of the xV2O5.(100-x)[Bi2O3.B2O3] glass system is analyzed using two spectroscopic methods, namely FT-IR absorption spectroscopy and Electron Paramagnetic Resonance spectroscopy (EPR). The samples, in the compositional range 0 – 50 mol % V2O5, were prepared by melt-quenching technique.
The presence of the main bismuthate and borate structural units [BiO3], [BiO6], [BO3], [BO4] and their dependence on the V2O5 content are discussed using IR spectral analysis. The presence of the IR absorption bands assigned to Bi2O3 proves the role played by this unconventional glass network former in the structure of the samples. The characteristic vibrations of the boroxol rings are also evidenced. 
EPR spectra were recorded at room temperature for the entire compositional range. The spectra contain a resonance line centered at g1.9 with a partially resolved 51V (I=7/2) hyperfine structure for the samples with x>30 mol % V2O5. This fact provided evidence for the existence of the isolated paramagnetic V4+ ions, whose resonance line overlaps with the broad line characteristic to the clustered V4+ ions.