Evidence of Intermediate Phase in (Na$_{2}$O)$_{x}$(GeO$_{2}$)$_{1-x}$ glasses

Intermediate phases have been observed in covalent glasses, but ionically bonded network systems have received much less attention in this respect. We have now examined titled glasses in m-DSC, Raman scattering, IR reflectance and Birefringence experiments over wide range of soda concentration, 3 $<$ x $<$ 30{\%}. Thermal experiments reveal a sharp reversibility window (RW) in the 14{\%} $<$ x $<$ 19{\%} soda range, which correlates well with a broad global maximum in molar densities (germanate anomaly) . Raman and IR reflectance TO and LO mode frequencies exhibit anomalies between x$_{c}$(1) = 14{\%} (\textit{stress} transition) and x$_{c}$(2) = 19{\%} (\textit{rigidity} transition), with optical elasticity power-laws confirming the nature of the transitions. Birefringence measurements dramatize the macroscopically stress-free nature of the Intermediate Phase (IP) in the RW. These data also suggest that the germanate anomaly can be understood as a direct consequence of the multiscale structural self-organization of glasses in the IP.