Influence of MgO (CaO) on the structure of silicate-phosphate glasses

Thermal and structural properties of model silicate-phosphate glasses containing the different amounts of the glass network modifiers, i.e. Mg²⁺ and Ca²⁺ were studied. To explain the changes of the parameters characterizing the glass transition effect (T_g, Δc_p) and the crystallization process (T_c, ΔH) depending on the cations modifiers additions, analysis of the bonds and chemical interactions of atoms in the structure of glasses was used. ³¹P MAS-NMR spectra of SiO₂–P₂O₅–MgO(CaO)–K₂O glasses show that the phosphate complexes are mono- and diphosphate. It has been found that increasing amounts of Mg²⁺ or Ca²⁺ cations in the structure of glasses causes the reduction of the degree of polymerization of the phosphate framework (Q¹→Q⁰). The influence of increasing of modifiers in the structure of silicate- phosphate glasses on the number of non-bridging oxygens per SiO₄ tetrahedron and density of glasses was presented.