Raman spectroscopy studies of xNa2S+(1−x)B2S3 glasses and polycrystals

The Raman spectra of binary xNa2S+(1−x)B2S3 glasses and polycrystals have been measured for the first time and are used to develop a structural model of the sodium thioborate glasses. The Raman spectra confirm our previous infrared (IR) experimental conclusions that the structure of vitreous (ν-B2S3) is comprised of B3(0) groups and six-membered rings. It was also found that as sodium sulfide is added to the glass in the low alkali (x<0.35) glass forming region, the B4 groups are formed at the expense of the B3(0) groups first and then from the six-membered ring groups. The Raman spectra are also consistent with the presence of a pyramidal structural arrangement of B4 groups with trigonally coordinated sulfur atoms. This structure could explain the existence of the super-stoichiometric amounts of B4 groups found using nuclear magnetic resonance (NMR). Glasses in the high alkali region (0.50<x<0.80) progressively change from being comprised of metathioborate rings to being comprised of B3(3) groups. The Raman spectra also confirms the IR spectra which saw no evidence of B3(2) groups in these sodium thioborate glasses.