Glass transition temperatures and mass densities of binary vanadate glasses in the context of the structural characteristics

Glass transition temperatures ( T g ) and mass densities (ρ) for binary alkali and alkaline earth vanadate glasses—determined in this study or reported in a previous paper—are discussed to clarify the structural reasons for the property changes. A notable difference exists between the continuous increase in T g for alkaline earth modifiers (MO) and the T g minima observed for alkali modifiers (A 2 O). Densities are analyzed based on the packing fraction, ρ P . A uniform trend in ρ P is characteristic of glasses containing A 2 O. In contrast, the ρ P values for each MO addition show specific behavior. Starting from vitreous V 2 O 5 , which contains about 50 % VO 5 pyramids, the modifier cations A + and M 2+ are proposed to coordinate terminal and bridging oxygen atoms differently. At glasses approaching 50 mol% V 2 O 5 , the need for charge balance and spatial accommodation of the modifier cations results in solely VO 4 chain units, regardless of whether the modifiers are alkali or alkaline earth oxides.