INFRARED-SPECTROSCOPY OF WIDE COMPOSITION RANGE XNA2S+(1-X)B2S3 GLASSES

Wide composition range studies of the IR spectra of xNa2S + (1 - x)B2S3 glasses are reported for the first time. Glasses can be prepared in two composition regions: 0 less-than-or-equal-to x less-than-or-equal-to 0.33 in a low-alkali region and 0.55 less-than-or-equal-to x less-than-or-equal-to 0.80 in a high-alkali region. The structures of glasses in the former region are dominated by the creation of tetrahedral boron units similar to those observed in the alkali borate glasses. For pure B2S3, a large fraction of six-membered rings is found, as in glassy B2O3. As alkali is added, the vibrational frequency of the six-membered ring mode decreases, but not the intensity, and a new band grows in which is used to propose, by analogy with the alkali borate glasses, that the fraction of tetrahedral borons increases with alkali sulfide content. These observations suggest that isolated six-membered rings persist even in the presence of tetrahedral borons. For the high-alkali glasses, both the six-membered rings and tetrahedral boron structures are destroyed in preference to the formation of isolated orthothioborate groups, Na3BS3. The IR spectra of the high-alkali glasses show a monotonic increase in symmetry and simplicity, indicating an increase in structural simplicity as the orthothioborate composition is approached. For the orthothioborate composition, both glass and polycrystal can be prepared. The IR spectra of the two phases are very similar, with the glass exhibiting a broadened absorption envelope.