Rigidity transitions in binary Ge–Se glasses and the intermediate phase

Raman scattering measurements, undertaken on bulk GexSe1−x glasses at 0<x<1/3, show evidence of two rigidity transitions as monitored by compositional trends in corner-sharing (νCS) and edge-sharing (νES) Ge(Se1/2)4 mode frequencies. A second-order transition from a floppy to an unstressed rigid phase occurs near xc(1)=0.20(1) where both νCS(x) and νES(x) show a kink. A first-order transition from an unstressed rigid to a stressed rigid phase occurs near xc(2)=0.26(1), where νCS2(x) displays a step-like discontinuity between x=0.25 and 0.26 and a power-law behavior at x>xc (2). In sharp contrast, earlier micro-Raman measurements that use at least three orders of magnitude larger photon flux to excite the scattering, showed only one rigidity transition near xc=0.23, the mid-point of the intermediate phase (xc(1)<x<xc(2)). Taken together, these results suggest that the intermediate phase, observed in the low-intensity Raman measurements, undergoes a light-induced melting to a random network in the micro-Raman measurements.