Fig. 3b shows the deconvoluted Raman spectra of quenched glasses. The peaks centered at 572 cm−1 in glass#2Bi2O3 and 556 cm−1 in glass#9Bi2O3 can be ascribed to the vibration of [BO4] units25; whereas, the peaks located at 1398 cm−1 in glass#2Bi2O3 and 1335 cm−1 in glass#9Bi2O3 can be associated with the vibration of [BO3] units.
25,26 This indicates that boron presents in [BO3] and [BO4] units in
glass structure in present work. It is clear that the peak corresponding for the B O B bending of [BO3] units27 can only be observed at 705 cm−1 in glass#2Bi2O3. In addition,the peak associated with [BO4] units26,28 present at 735 cm−1
in glass#9Bi2O3 not glass#2Bi2O3. It is also worth noting that
the ratio of [BO4]/[BO3] increases from 1.5 for glass#2Bi2O3
to 16 for glass#9Bi2O3, indicating that Bi2O3 dopant significantly enhances the [BO3] → [BO4] transition in glass structure
in present work. Kaur et al. also reported that the addition
of Bi2O3 (from 5 to 25 mol.%) in Bi2O3–Na2O–B2O3–SiO2
glass system causes a progressive conversion of [BO3] to
[BO4] units leading to increase of the strength of the glass
structure and interconnection of the structural units.
13 Considering the much greater stability of [BO4] compared with
that of [BO3], the [BO3] → [BO4] transition in glass structure contributes to the reduced boron volatility in present
work.