Effects of MgO/CaO on the structural, thermal and dielectric properties of aluminoborosilicate glasses

Glasses with compositions xMgO-(20?x)CaO-10Al₂O₃-20B₂O₃-50SiO₂ (x = 0, 5, 10, 15 and 20 mol%) were prepared by conventional melting method. X-ray photoelectron spectroscopy (XPS) results indicated that the proportion of non-bridging oxygen increased with increasing MgO content. Nuclear magnetic resonance spectra showed that the fraction of the four-coordinated boron ions N_4(B) and aluminum ions N_4(Al) decreased with increasing MgO/CaO. Thus, higher field strength cations were expected to weaken the glass network. However, the increase in the glass transition temperature (T_g) indicated that the magnesium ions strengthened the glass network. The decrease in dielectric constant ε_r and loss tanδ could be attributed to the increase in the rigidity of the glass network as the MgO content increased.