Progress, Challenges, and Rewards in Probing Melt Dynamics, Configurational Entropy Change, and Topological Phases of Group V‐ and Group IV‐Based Multicomponent Sulfide Glasses

Abstract

The observation of reversibility windows (RWs) in binary GexS100−x, AsxS100−x and ternary GexAsxS100−2x glass systems permits constructing a global topological phase diagram in the GeAsS composition triangle. The RW denotes glass compositions for which the enthalpy of relaxation at Tg vanishes, leading to thermally reversing glass transitions. The phase diagram permits delineating glass compositions that are in the flexible phase (FP), intermediate phase (IP), and the stressed rigid phase (SRP) for all ternary GexAsxS100−2x glass compositions. For the IP compositions examined, a general lowering of the molar volumes, Vm, is observed in relation to those for non‐IP compositions, giving rise to a volumetric window. Melt dynamics of IP compositions reveal a fragility index, m < 20, lower than that for non‐IP melts for which m > 20 displays a fragility window, underscoring in part the reason for the delayed homogenization of melts in these sulfide glasses. The observations of the three types of window characteristics of IP compositions are feasible only when the homogeneous bulk glasses are synthesized, in which the variance ⟨Δx⟩ in As and Ge concentrations, x, across batch compositions is less than 0.01%. This is established by Fourier transform–Raman profiling of each batch of composition that is synthesized.

Analytical model of the network topology and rigidity of calcium aluminosilicate glasses

“…We then focus on the relationship between molar volume ( V m ) and n c . Indeed, it has previously been observed that ideally connected isostatic glasses (especially chalcogenide glasses) exhibit an optimal space‐filling tendency, which manifests itself as a minimum in molar volume 79–85 . Interestingly, we find that V m exhibits a fair minimum around n c = 2.75, which is close to the isostatic threshold (Figure 8B).…”

“…Indeed, it has previously been observed that ideally connected isostatic glasses (especially chalcogenide glasses) exhibit an optimal space-filling tendency, which manifests itself as a minimum in molar volume. [79][80][81][82][83][84][85] Interestingly, we find that V m exhibits a fair minimum around n c = 2.75, which is close to the isostatic threshold (Figure 8B). This suggests that the optimal space-filling tendency of isostatic glasses might a be generic feature of the glassy state.…”

“…This is motivated from the fact that several chalcogenide and oxide glasses have been noted to exhibit a minimum in melt fragility around their isostatic threshold. [81][82][83][84][85][86] Although the lack of available experimental data prevents us from being fully conclusive, we do observe a strong correlation between m and n c -wherein flexible glasses (n c < 3) exhibit larger fragility values than their isostatic counterparts (Figure 8C). Additional measurements in the stressed-rigid domains (n c > 3) would be needed to test the existence of a minimum of fragility in this system.…”

A Lattice Litany for Transition Metal Oxides

“…The inhomogeneities appear on well-defined length scales and can be compared to the formation of intrinsic mesoscopic metastable patterns found in two-fluid I conclude this section with a more general perspective on multiscale landscapes resulting from coexisting short-long-range interactions. In particular, the appearance of glassy filamentary phases in windows of intermediate doping concentration ("intermediate phases") [62,63] is demonstrated in [64,65] as a model of doped 2D anti-ferromagnets. I believe these intermediate phases are very important functionally and should be realized in many materials, including doped TMOs.…”

“…Hence, if atomic configurations are allowed to relax self-consistently in a Coulomb field, the elasticity features above must be recovered. Finally, we note that a quite general framework for intermediate phases can be expressed in a theory describing network adaptability and rigidity transitions based on the degree of lattice connectivity and the number of bonding constraints [62,63,69]. The next material frontiers must include understanding reactive networks.…”