The scaling of Vickers hardness (Hv) in oxide glasses with varying network modifier/modifier ratio is manifested as either a positive or negative deviation from linearity with a maximum deviation at the ratio of about 1:1. In an earlier study [J. Kjeldsen et al., J. Non-Cryst. Solids 369, 61 (2013)], we observed a minimum of Hv in CaO/MgO sodium aluminosilicate glasses at CaO/MgO = 1:1 and postulated that this minimum is linked to a maximum in plastic flow. However, the origin of this link has not been experimentally verified. In this work, we attempt to do so by exploring the links among Hv, volume recovery ratio (VR) and plastic deformation volume (VP) under indentation, glass transition temperature (Tg), Young's modulus (E), and liquid fragility index (m) in CaO/MgO and CaO/Li2O sodium aluminosilicate glasses. We confirm the negative deviations from linearity and find that the maximum deviation (i.e., the so-called mixed modifier effect) of Hv, Tg, and m is at the modifier ratio of 1:1. These deviations increase in intensity as the total modifier concentration increases. We find a strong correlation between VP and Hv for the CaO/MgO series, implying that the minimum in Hv originates primarily from an increased shear flow in the mixed modifier glasses.

While the mixed alkali effect has received significant attention in the glass literature, the mixed alkaline earth effect has not been thoroughly studied. Here, we investigate the latter effect by partial substitution of magnesium for calcium in sodium aluminosilicate glasses. We use Raman and NMR spectroscopies to obtain insights into the structural and topological features of these glasses, and hence into the mixed alkaline earth effect. We demonstrate that the mixed alkaline earth effect manifests itself as a maximum in the amount of bonded tetrahedral units and as a minimum in liquid fragility index, glass transition temperature, Vickers microhardness, and isokom temperatures (viz., the temperatures at η = 10 13.5 and 10 12.2 Pa s). The observed minima in fragility, glass transition temperature, and isokom temperature are ascribed to bond weakening in the local structural environment around the network modifiers. We suggest that, since the elastic properties of the investigated system are compositionally independent, the minimum in Vickers microhardness is closely correlated to the minimum in isokom temperatures. Both of these properties are related to plastic flow and the translational motion of structural units, and hence both may be related to the same underlying topological constraints. This indicates that there might not be any significant difference in the onset of the rigid sub-T g constraints for the investigated compositions.

Revealing and understanding the microscopic origins of the macroscopic properties of aluminosilicate glasses is important for the design of new glasses with optimized properties. In this work, we study the composition‐structure‐property relationships in 20 MgO/CaO sodium aluminosilicate glasses upon Al2O3‐for‐SiO2 and MgO‐for‐CaO substitutions. We find that some properties (density, molar volume, Young's modulus, and shear modulus) are linear through the investigated range of Al2O3 compositions, while others (refractive index, coefficient of thermal expansion, Vickers hardness, isokom temperatures, and liquid fragility index) exhibit a change in the slope around the composition with [Al2O3] = [Na2O], which is especially pronounced for the glasses containing MgO. We discuss these phenomena based on structural information obtained by NMR spectroscopy and topological considerations.

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Transition metal containing glasses have unique electrical properties and are therefore often used for electrochemical applications, such as in batteries. Among oxide glasses, vanadium tellurite glasses exhibit the highest electronic conductivity and thus the high potential for applications. In this work, we investigate how the dynamic and physical properties vary with composition in the vanadium tellurite system. The results show that there exists a critical V(2)O(5) concentration of 45 mol %, above which the local structure is subjected to a drastic change with increasing V(2)O(5), leading to abrupt changes in both hardness and liquid fragility. Electronic conductivity does not follow the expected correlation to the valence state of the vanadium as predicted by the Mott-Austin equation but shows a linear correlation to the mean distance between vanadium ions. These findings could contribute to designing optimum vanadium tellurite compositions for electrochemical devices. The work gives insight into the mechanism of electron conduction in the vanadium tellurite systems.