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Abstract The Q‐speciation and the role of modifier dynamics on network relaxation in the supercooled mixed‐alkali–alkaline‐earth (MAAE) Na–Ba metaphosphate liquids are investigated using a combination of³¹P nuclear magnetic resonance (NMR) spectroscopy, calorimetric, electrical conductivity, and rheological measurements. Progressive replacement of Na with Ba in these glasses is shown to result in an increasing disproportionation of Q²species via the reaction: 2Q² = Q¹+ Q³. Unlike mixed‐alkali liquids, the Na–Ba metaphosphate liquids display a monotonic variation in isothermal electrical conductivity, glass transition temperature, calorimetric and kinetic fragility, and isothermal viscosity. It is hypothesized that this monotonic variation arises from the lack of elastic facilitation of network relaxation via coupled hopping of Na–Ba pairs as these modifier cations are prohibited from mixing randomly due to the differences between their size, mass, charge, and mobility. Isobaric heat capacity measurements provide supporting evidence in favor of a such a nonrandom mixing between the modifier cations in Na–Ba metaphosphate glasses and liquids. 

Abstract The impact of microstructure on hardness in phase‐separated calcium aluminosilicate glasses is investigated. Changes in hardness are governed by microstructure deformations that occur during indentation. Phase separation leads to decreased hardness due to the incongruent yielding of the droplet and matrix phases. Moreover, the deformation of microstructures possessing dilute, spherical droplets did not have a significant impact on hardness. Microstructures characterized by concentrated, acicular droplets were found to deform through a process of droplet coalescence. This process absorbs additional energy during yielding and results in glasses that deform through droplet coalescence possessing improved hardness. 

Abstract Glasses with nanoscale phase separation have the potential to possess improved hardness and fracture toughness while maintaining their optical transparency. Here we present the results of isothermal heat treatments of phase‐separated calcium aluminosilicate glasses. Our results indicate that a transition from Lifshitz–Slozof–Wagner (LSW)‐type kinetics to a diffusion‐controlled pseudo‐coalescence mechanism occurs at ~17% droplet volume fraction, which results in the droplets becoming increasingly elongated and interconnected. The activation barrier for both mechanisms suggests that calcium diffusion is the underlying means for the coarsening of the silica‐rich domains. Simple approximations show the transition cannot be explained by Brownian motion or Van der Waals attraction between domains, and instead suggest various osmotic forces may be responsible.