Study of potassium-zinc borophosphate glasses

Potassium-zinc borophosphate glasses were prepared and studied in two compositional series xK₂O-(50−x)ZnO-10B₂O₃-40P₂O₅ and xK₂O-(50−x)ZnO-20B₂O₃-30P₂O₅ with x=0, 10, 20, 30, 40 and 50 mol% K₂O. The replacement of zinc by potassium decreases the density and increases the molar volume of these glasses, whereas glass transition temperature and chemical durability decrease with increasing potassium content. Structural changes were studied by ¹¹B and ³¹P MAS NMR and Raman spectroscopy. The observed changes in the spectra and the properties of the studied glasses can be ascribed to several reasons and namely to the differences in the space occupied by cations Zn²⁺ and 2K⁺, the differences in the electronegativity of zinc and potassium and a large difference in the field strength of Zn²⁺ and K⁺ cations and thus higher ionicity of K-O bonds in comparison with Zn-O bonds.