A RAMAN INVESTIGATION OF LEAD HALOBORATE GLASSES

Glasses of the (65 - x)PbO.xPbX(2).35B(2)O(3) system (where X=F, Cl, Br, and I) have been made and investigated by Raman measurements. Three low frequency bands with high Raman intensities have been observed at about 40, 105, and 135 cm(-1), respectively. It is found that the intensities of the depolarized low frequency Raman contour peaked at 40 cm(-1) are exceptionally high and strongly dependent on the halogen type and content. We attribute this nonsymmetric low-frequency Raman contour to the collective modes of the BO3-PbO4 bridged local structures and propose a model to interpret the experimental data. Our, results suggest that the liberation of these local structures is related to the lead as well as the halogen. Cl, Br, and I enter the glass as nonbridging anions and weaken the cohesion of the glass network in the increased order of Cl, Br, and I.