Structure and glass transition temperature of sodium-silicate glasses doped with iron

•Qn species quantity determined by NMR and RS in iron-doped sodium-silicate glasses•Some correlations between Tg and changes in structure revealed•Glass transition temperature for investigated glasses decreases with pressure.•Tg vs. iron content behaved unusual in range with low iron content.

Glass transition temperature (Tg) of iron-doped sodium silicate glasses (100 − x)Na2O ⋅ xSiO2⋅ yFe2O3 (x = 75, 78, 81 mol%, y = 0.1–17 wt.%) were determined by DSC method under different pressure (101.325, 5000, 10,000 kPa). DSC experiment showed nonmonotonic behavior (with dominating growth) of Tg and its changes under pressure for iron-doped glass with total iron content. 29Si NMR of glasses with x = 75; 81 and y up to 2.75%, and Raman spectroscopy were applied for Qn structural units estimation. In NMR spectra two signals are detected, average values of the shifts − 105 ppm and − 93 ppm, corresponding to Q4 and Q3. Quantities of the Q4 and Q3 units were achieved from spectra fitting, the last one rising with total iron content. Three bands (960–1000 cm− 1, 1080–1100 cm− 1, 1120–1170 cm− 1) were detected in Raman spectra, assigned as vibrations in Q3 (Si net with Fe), Q3(Si) and Q4(Si) respectfully. Specialties in Tg behavior with total iron content correlates with intensity of 1080–1100 cm− 1 bands in Raman spectra, 960–1000 cm− 1 band intensity grows proportionally with total iron content. Relative band intensities were used to make half-quantitative calculations of Qn content in glasses with high iron content. These estimations are compared with calculations from Zachariasen rules, revealing change in Fe(III) role from modifier to net-former.