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.