Reflectivity spectra of TeO₂-PbCl₂ glasses

Five samples of red coloured (TeO₂)_1-y(PbCl_2-zO_z/2)_y glasses (y = 0.17; 0.19; 0.34; 0.44; 0.64 and z/2 = 0.40-0.64) were prepared from TeO₂ and PbCl₂ starting compounds by melting in platinum crucibles. Results of chemical analysis revealed that a substitution reaction had proceeded in the course of glass preparation yielding lead oxide which was built into the glass network. The glass samples were subjected to measurements of reflectivity spectra in the range 70-1000 cm^-1 at ambient temperature. In the range of low wavenumbers a band was found at around 85 cm^-1 corresponding apparently with vibrations of Pb-Cl bonds; a shoulder in the range 110-115 cm^-1 was attributed to vibrations of infrared active modes of PbO. In the range 300-750 cm^-1 the reflectivity spectra of investigated samples showed some similarity to spectra of crystalline tellurites and tellurite glasses. In this range four bands were observed which were related to vibrations of TeO bonds in TeO₃ trigonal pyramids (TPs) and TeO₄ trigonal bipyramids (TBPs) in the tellurite glass network. The reflectivity spectra were fitted by the harmonic oscillator method; wavenumbers dependencies of the absorption coefficient K in the studied spectral range were determined using the oscillator parameters obtained from the fits. A comparison of the TeO₂-PbCl₂-PbO absorption spectrum with a tellurite glass spectrum showed that a gradual building of PbO into the glass network results in a decrease in the concentration of the TeO₄ TBPs while the participation of the TeO₃ TPs increases. The evaluation of the TeO₂-PbCl₂-PbO reflectivity spectra with respect to results of chemical analysis allowed one to formulate a conception of structural entities forming the TeO₂-PbCl₂ glass network.