Composition dependence of glass transition temperature and fragility. II. A topological model of alkali borate liquids

Abstract

Glass transition temperature and fragility are two important properties derived from the temperature dependence of the shear viscosity of glass-forming melts. While direct calculation of these properties from atomistic simulations is currently infeasible, we have developed a new topological modeling approach that enables accurate prediction of the scaling of both glass transition temperature and fragility with composition. A key feature of our approach is the incorporation of temperature-dependent constraints that become rigid as a liquid is cooled. Using this approach, we derive analytical expressions for the composition (x) dependence of glass transition temperature, T(g)(x), and fragility, m(x), in binary alkali borate systems. Results for sodium borate and lithium borate systems are in agreement with published values of T(g)(x) and m(x). Our modeling approach reveals a natural explanation for the presence of the constant T(g) regime observed in alkali borate systems.

Crucial effect of melt homogenization on the fragility of non-stoichiometric chalcogenides

“…It has been shown that T g is an accurate measure of network connectivity [59][60][61] and follows very precisely any coordination change induced by chemical alloying. This is not only true for chalcogenides but also for binary oxides such as alkali germanate or borate glasses for which a maximum in T g is obtained when the population of some higher-coordinated species maximizes with modifier content 31,55,62 . Ultimately, it is seen that the change from a negative to a positive correlation is strongly tied to the minimum found for the fragility index M (Fig.…”

Structure of molten titanium dioxide

“…8, full precision trend given in Fig. 8 caption, see also Melt fragility measures the degree of deviation from Arrhenian behavior of the liquid viscosity, and has been directly related to the temperature dependence of the number of degrees of freedom per atom [61][62][63]. Hence the observed temperature dependence of the coordination numbers is expected to contribute to an increased liquid fragility, as well as to the large thermal expansion coefficient (see Table III and Fig.…”

Topological Model for Boroaluminosilicate Glass Hardness

“…When n > 3, the network is "stressed rigid" due to its high connectivity, whereas the isostatic state is achieved for n = 3. The theory has later been extended by Gupta and Mauro to account for the temperature dependence of the constraints Mauro et al, 2009), allowing for a distinction of the individual constraints based on their chemistry via the constraint onset temperature. Here, we derive a topological hardness model for sodium boroaluminosilicate glasses and validate it against experimental measurements for three distinct series of glasses.…”

“…In this work, we attempt to apply the hardness model of Smedskjaer et al (2010a) based on topological constraint theory Mauro et al, 2009;Smedskjaer et al, 2010b;Micoulaut, 2011, 2013;Jiang et al, 2013;Rodrigues and Wondraczek, 2013) to predict the composition dependence of sodium boroaluminosilicate glass hardness. The model has been found to be quantitatively predictive for borate glasses (Smedskjaer et al, 2010a,c), borosilicate glasses (Smedskjaer et al, 2011), phosphosilicate glasses (Zeng et al, 2014), and calcium silicate hydrates (Bauchy et al, 2014), but has not yet been tested for a system with three network-forming oxides.…”