Vibrational spectroscopic and computational studies of sol–gel derived CaO–MgO–SiO2 binary and ternary bioactive glasses

In this work we report on a vibrational spectroscopic study on the structural aspects of the binary xCaO·(100 − x)SiO2, xMgO·(100 − x)SiO2 and ternary xCaO·yMgO (100 − x − y)SiO2 systems for various x values up to 50%. Raman and IR spectroscopies have revealed the degradation of the silica network with the addition of the oxide modifiers. The main differences in the spectra of the alkaline earth modified sol–gel glasses are located in the region 900–1200 cm−1 where vibrations of SiO4 tetrahedra with a variable number of non-bridging oxygen atoms are located. A comparison between the structural modifications of bulk (melt-quenched) and porous glasses is also advanced revealing particular differences in the network modification of the two types of glasses. CaO is more drastic than MgO in depolymerizing silica's network and both of them cause more significant structure modifications in the sol–gel glasses. The depolymerization structural units offer the appropriate sites in the glass network that are responsible for the facilitation of Ca/Mg dissolution, which is an important step for bioactivity. Furthermore, to support the conclusions drawn from the experimental data, preliminary molecular structure simulations using semiempirical molecular orbital theory are also presented.