Topological Phases of Chalcogenide Glasses Encoded in the Melt Dynamics

Abstract

Select Raman scattering and modulated differential scanning calorimetry (DSC) experiments on specially homogenized binary GexSe100–x and GexS100–x chalcogenide glasses, supported by ab initio MD simulations are undertaken. In both chalcogenides, the glasses exhibit a super‐strong behavior (with a melt fragility index, m(x) < 20) in the 20(1)% < x < 26(1)% composition range, defining the fragility window, and with m(x) > 20 as one goes away from the fragility window. Remarkably, molecular dynamics (MD) simulations confirm the existence of the fragility window. Furthermore, in both chalcogenide glasses, the enthalpy of relaxation at Tg, ΔHnr(x), becomes minuscule (≈0) in the 20(1)% < x < 26(1)% range, defining the reversibility window, and with ΔHnr(x) increasing by an order magnitude abruptly with x outside that window. Thus, super‐strong melts formed in the fragility window give rise to isostatically rigid glasses in the reversibility window and fragile melts formed at x < 20(1)% and at x > 26(1)% give rise to flexible‐ and stressed‐rigid glasses, respectively. Melt dynamics for the examined glass systems unequivocally encode the nature of the glass topological phases.

Intermediate Phase in Calcium–Silicate–Hydrates: Mechanical, Structural, Rigidity, and Stress Signatures

“…These results suggest that the intermediate phase is encoded in the medium-range (rather than short-range) order structure of C-S-H. The fact that the typical repetition distance is minimum in the intermediate phase can be related to the fact that intermediate-phase glasses have been shown to exhibit an optimal space-filling tendency (for instance, several chalcogenide glasses exhibit a minimum in molar volume in the intermediate phase) (Rompicharla et al, 2008;Boolchand et al, 2018). This can be understood from the fact that, due to their low connectivity, flexible networks tend to present large rings or terminating bonds, which decreases the packing efficiency of the atoms.…”

“…Interestingly, isostatic chalcogenide glasses belonging to the intermediate phase exhibit some unique properties, namely a reversible glass transition (Boolchand et al, 2001;Chakravarty et al, 2005), weak relaxation and aging (Chakravarty et al, 2005;Chen et al, 2010), low propensity for creep (Bauchy et al, 2017), anomalous mechanical properties (Varshneya and Mauro, 2007;Bauchy et al, 2016a), superstrong behavior (Boolchand et al, 2018), optimal space-filling tendency (Phillips, 2006;Rompicharla et al, 2008), and stress-free character (Wang et al, 2005).…”

Evidence for a Correlation of Melt Fragility Index With Topological Phases of Multicomponent Glasses

“…It helps one understand how homogeneity of melts/glasses is intimately tied to the observation of the IP in these glasses. Melt/glass homogenization is precursive to observation of a sharp squarewell like reversibility window permitting one to fix the three TPs (Boolchand et al, 2018).…”

Emerging role of local and extended range molecular structures on functionalities of topological phases of (Na2O)x(P2O5)100‐x glasses using Raman scattering and modulated DSC

“…These phases have now been observed in Chalcogenides‐, 6,7 , modified oxides, 8,9 , Heavy metal oxide‐, 10 and Solid electrolyte 11 glasses. Recent studies have further revealed that melt dynamics 12 are closely correlated to these phases, with super‐strong melts giving rise to IP glasses upon cooling to T g .…”

“…Our results show that in the IP the molecular structure is dominated by LCs with LRs and SRs comprising a minority. The result permits one to reconcile the high configurational entropy of that phase, which leads that phase to display qualitatively suppressed aging 13 or high stability 12,22 . In section 2 we discuss the Materials and Methods followed by the experimental results in Section 3, and select salient issues discussed in Section 4.…”