SHORT AND INTERMEDIATE RANGE STRUCTURES IN FLUORIDE GLASSES BY VIBRATIONAL SPECTROSCOPY

Recent developments in the study of the structure of fluoride glasses are presented for the case of two-component and multi-component ZrF4-based glasses and also for more ionic glasses such as those based on ZnF2-CdF2, with particular emphasis on vibrational spectroscopy results, especially on the detection of transverse optic-longitudinal optic (TO-LO) pairs in those glasses by infrared reflection spectroscopy at oblique incidence. The approximate positions of TO-LO vibrational pairs have been determined for different compositions in these glass systems by FTIR specular reflectivity at incidence angles between 10 and 60-degrees off-normal. These results are compared with TO and LO spectra calculated for those glasses by Kramers-Kronig analysis and they are interpreted in terms of short and intermediate range order. Polarized Raman spectra were also studied for the same glasses at low frequencies, using Martin and Brenig's acoustic model, from which some intermediate range structural information was derived. The observed level of intermediate range order appeared to correspond to the most probable distributions of the bridging and dihedral angles. These data are compared with results for other halide and oxide glass systems.