A new approach to determine and quantify structural units in silicate glasses using micro-reflectance Fourier-Transform infrared spectroscopy

Eight silicate unit vibrational modes were identified in a suite of PbO-SiO 2 glasses using micro-reflectance Fourier Transform infrared (μR-FTIR) spectra that were transformed using the Kramers- Kronig relation. The transformed FTIR spectra, in the 800-1200 cm -1 range, were deconvolved systematically into eight Voigt-shaped bands at centers that were predicted from the second derivative of the spectra. The area of the eight bands varied as a function of SiO 2 content, and these trends were combined with theoretical constraints to identify and assign the bands to seven provisional silicate units: SiO 4 4- (830 and 860 cm -1 ), Si 2 O 7 6- (900 cm -1 ), Si 6 O 18 12- (950 cm -1 ), Si 2 O 6 4- (980 cm -1 ), Si 4 O 11 6- (1010 cm -1 ), Si 2 O 5 2- (1050 cm -1 ), and SiO 2 (1100 cm -1 ). The provisional units were then grouped according to their NBO/T values: NBO/T = 4 (SiO 4 4- ), NBO/T = 3 (Si 2 O 7 6- ), NBO/T = 2 (Si 6 O 18 12- and Si 2 O 6 4- ), NBO/T = 1 (Si 4 O 11 6- and Si 2 O 5 2- ) and NBO/T = 0 (SiO 2 ). The derived quantities of each NBO/T unit compare favorably with nuclear magnetic resonance data for PbO-SiO2 glasses reported in the literature. This new approach for determining glass structure is advantageous because it may be performed on small Fe-bearing samples with minimal preparation, and analyses are rapid and relatively inexpensive.