Structural investigation and physical properties of Ga2O3-ZnO-P2O5 glasses

Glasses with composition xGa2O3-(50-x)ZnO-50P2O5 (where x = 0-30) were prepared, and their basic physical characteristics (density, molar volume, glass transition and softening temperatures, thermal expansion coefficient and microhardness) were measured and discussed in connection with structural changes. Raman spectroscopy and 31P MAS NMR showed that increasing substitution of zinc(II) by gallium(III) shifts the basic structure of the glass from the prevailing metaphosphate (Q2) to pyrophosphate (Q1). With the highest content of gallium (x = 30), orthophosphates (Q0) appear, which ultimately leads to crystallization of GaPO4 in the glassy matrix. Therefore, glass with x > 25 could not be prepared, even with rapid cooling. 71Ga MAS NMR showed that at a lower Ga concentration, the dominating metaphosphate structure gallium was primarily six-coordinated, whereas with the dominating pyrophosphate structure (x ≥ 10), four-fold coordinated Ga prevailed.