Infrared study of the effect of P2O5 in the structure of lead silicate glasses

The infrared spectra of xPbO (1-x-z)SiO(2)zP(2)O(5) glasses with a PbO:SiO2 molar ratio of 3:2 and z=0,1,2,5,30,40 and 50 mol% have been examined in the region 4000-400 cm(-1), together with XRD. The structure of PbO-SiO2 binary glass is significantly different from that of P2O5 substituted glasses. The low amount of P2O5 containing PbO-SiO2 glasses results in infrared spectra of the same pattern as 3:2 binary lead silica glass but the maximum peak intensities and positions are different. The spectra of high P2O5 (30-50 mol%) containing glasses show an increased number of distinct peaks in the low frequency region with a convolution of several broad Gaussians in the high frequency region. All the spectra are base line corrected and deconvoluted to appropriate number of Gaussians. The peaks and peak positions of the Gaussians are assigned to Si-O-Si, Si-O-Pb, Si-O-P, P-O-P, O-P-O, P=O, P-O- etc. bonds. A variation in the band positions and the relative amounts of bonds with P2O5 is also shown. The result indicates that ortho- and pyro-phosphate are formed around 1-5 mol% P2O5 containing glasses and meta-phosphate species from the high P2O5 containing glasses. The ionic character of the phosphate groups P-O-, PO43- is well revealed by the formation of new band within 1250-900 cm(-1). The incorporation of high contents of P2O5 in the materials suggests that P5+ occupies the network position and forms the linkage Si-O-P in the glasses. This Si-O-P bond may lead to the formation of five and six coordinated silicon in the glass matrix. X-ray diffraction pattern of the base samples, within the detection limit, shows that all are homogeneous glasses and these have not shown any evidence of phase separation on optical inspection.