SODIUM BOROVANADATE GLASSES: STRUCTURE UP TO THE MELTING POINT FROM RAMAN SPECTROSCOPY

Sodium borovanadate glasses have been elaborated by splat cooling technique. Raman measurements on the un-doped or on the vanadium non-polished samples reveal the presence of tincalconite crystal (Na2B4O7-5H2O) and ?-NaVO3 crystal on the superficial layers respectively. After polishing, Raman spectra characteristic of glasses are obtained with two main bands located at 466 cm-1 and 774 cm-1 in the un-doped glass and four bands at 239, 374, 774 and 934 cm-1 for the vanadium oxide doped glasses. Thermal treatment up to 523?C of the borovanadate glass containing 20% V2O5 leads to separation in two phases enriched in vanadium and in boron with a ?-NaVO3 surface crystallisation. No bulk crystallization occurs before melting. PACS: 81.05.kf; 78.30.-Ly; 78.30.-j; 65.50.-x