Raman pressure effects and internal stress in network glasses

Intermediate phases are predicted to be unstressed elastic phases of network glasses. The case of binary Ge$_{x}$Se$_{1-x}$ glasses reveal the intermediate phase to reside in the 0.20 $<$ x $<$ 0.25 range$^{1}$. We have now performed$^{2}$ Raman scattering on Ge$_{x}$Se$_{1-x}$ glasses under pressure and find a steady increase in the frequency of modes of corner-sharing GeSe$_{4}$ tetrahedra when the external pressure P exceeds a threshold value P$_{c}$. The threshold pressure P$_{c}$(x) decreases with x to nearly zero for 0.20 $<$ x $<$ 0.25, then increases up to x = 1/3. P$_{c}$ indicates the presence of local stress at the Raman active units; so its vanishing suggests that these units are part of an isostatically rigid backbone. Isostaticity also accounts for the non-aging behavior of glasses observed in this same composition range$^{2}$ that is identified with the intermediate phase in this binary glass system. \newline \newline 1. P.Boolchand et al. JNCS \textbf{293-295}, 348 (2001). \newline 2. Fei Wang et al. Cond Matt 0408502 (to appear in Phys. Rev. B) \newline \newline Supported by NSF grant DMR-0456472 \newline