Direct evidence of rigidity loss and self-organization in silicate glasses

The Brillouin elastic free energy change Delta Phi between thermally annealed and quenched (Na2O)(x)(SiO2)(1-x) glasses is found to increase linearly for x > 0.23 (floppy phase), and to nearly vanish at x < 0.18 (stressed-rigid phase). The observed Delta Phi(x) variation closely parallels the mean-field floppy mode fraction f (x) in random networks, and fixes the two (floppy, stressed-rigid) elastic phases.. In calorimetric measurements, the non-reversing enthalpy near the glass transition temperature T-g is found to be large at x < 0.18 and at x > 0.23, but to nearly vanish in the 0.18 < x < 0.23 range, suggesting the existence of an intermediate phase between the floppy and stressed-rigid phases.