Intramolecular structural model for photoinduced plasticity in chalcogenide glasses

Selected spectral features of Raman spectra of glassy As₂S₃ subjected to elongation stress and sub-band-gap light illumination are analyzed and compared with polarization-dependent information obtained from the bulk glass at room temperature and near the glass transition temperature. The data are suggestive of specific structural changes which involve the transformation of atomic arrangements from realgarlike As₄S₄ molecules, originally present in virgin (untreated) fibers, into planar orpimentlike clusters. Implications of these atomic rearrangements to the incipient photoinduced fluidity---the onset of plastic deformation---in As₂S₃ glass are discussed. Kinetics of photoinduced plastic changes is compared to that of Raman spectra changes, revealing a qualitative similar behavior. An approximate estimation of the relative contribution of intermolecular rearrangements and the intramolecular structural mechanism proposed in this paper has revealed that the latter is responsible for almost 30% of the photoinduced elongation of the fiber's length at room temperature. The proposed mechanism can as well serve as rationale for understanding the photoinduced volume expansion observed in chalcogenide glasses.