COMPUTER-SIMULATION ON THE STRUCTURE AND VIBRATIONAL-SPECTRA IN GE-PB-O-F GLASS

Oxy-fluoride glasses in the GeO2-PbO-PbF2 system were prepared and their structure investigated using vibrational spectra, X-ray diffraction and Raman spectra methods. Structural models were constructed by molecular dynamics simulations. In the models obtained, grass networks were formed by GeO4 tetrahedra and Ge(O,F)(5) and Ge(O,F)(6) polyhedra. Lead entered the networks at Pb-F-Pb in the models with high Pb/Ge ratio. The presence of germanium with high coordination numbers of 5 and 6 was supported by radial distribution analyses. Ge-O bonds in GeO, tetrahedra seemed to give bands between 650 and 850 cm(-1) (non-bridging oxygen) and between 450 and 650, and between 850 and 950 cm(-1) (bridging oxygen). Ge-O and Ge-F in Ge(O,F)(n) (n > 4) were supposed to contribute the bands observed between 350 and 550 cm(-1) in the Raman spectra.