Structure and vibrational modes of AgI-doped AsSe glasses: Raman scattering and ab initio calculations

We report an investigation of the structure and vibrational modes of (AgI)x (AsSe)100−x, bulk glasses using Raman spectroscopy and first principles calculations. The short- and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometric-like and As-rich network sub-structures, and cage-like molecules (As4Sen, n=3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As4Sen molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As–I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSemI3−m provided useful information augmenting the interpretation of the Raman spectra.