Infrared Investigations of the Structure of Non-Oxide Chalcogenide Glasses
The structural nature of non-oxide chalcogenide glasses was investigated using infrared reflection and absorption techniques. The wave number corresponding to stretching mode vibrations for nine pairs of metal-chalcogen constituent atoms was identified using reflection and absorption spectra obtained from glasses representing fifteen chalcogenide glass systems containing IVA and/or VA elements. The validity of the vibrational assignments were verified by assuming them to represent simple diatomic stretching modes, applying Gordy’s simple diatomic force constant relation, and calculating the equilibrium interatomic distance for each bond pair. Comparison of calculated values with the sum of the appropriate covalent radii showed reasonable agreement in all cases, except for the As-S and As-Se vibrations, indicating the local symmetry for glasses containing these elements was different from the others. Using Somayajulu’s rule for calculating multi-bond force constants, the normal vibrational frequencies for nine constituent atom pairs were calculated for a X-Y2 linear symmetric triatomic configuration, a X-Y2 non-linear symmetric triatomic configuration, a X-Y3 pyramidal arrangement and a X-Y4 tetrahedral arrangement. Comparison between calculated and observed frequencies indicate that in most cases the IVA element forms a bridge between chalcogen atoms forming a X-Y2 non-linear symmetric triatomic configuration, while As in S and Se glasses exists in a pyramidal X-Y3 configuration.