Origin of the frequency shift of Raman scattering in chalcogenide glasses

Raman scattering is a sensitive method for probing the structural evolution in glasses, especially in covalent ones. Usually the main Raman scattering frequency shifts with composition for Gesingle bondSe chalcogenide glasses. However, it has not been well established whether and how the dependence of the shift is associated with the topological connectivity of global network and/or the local environment of structural units, (e.g., tetrahedral GeSe₄). Here we show the compositional evolution of the main Raman scattering frequency in Ge(S_xSe_1−x)₂ glasses, and then clarify its structural origin. We keep the number of topological constraints constant in the studied glass series, in order to explore the impact of mediate range structure on the main Raman scattering frequency. The results reveal that the frequency shift is attributed to the alteration of the nearest neighbor connectivity of central structural units such as GeS₄ tetrahedra. The ab-initio calculations of normal Raman mode combined with group theory analysis provide insight into the structural evolution of chalcogenide glasses with varying composition.