Effects of CaO/P2O5 ratio on the structure and elastic properties of SiO2–CaO–Na2O–P2O5 bioglasses

The evolution of elastic properties and structure upon the change of CaO/P2O5 ratio in SiO2–CaO–Na2O–P2O5 glasses (45S5-derived and 55S4-derived) at ambient conditions has been studied by using both Brillouin and Raman spectroscopy coupled with X-ray diffraction. Under the same SiO2/Na2O ratio, it is found that a decrease in CaO/P2O5 molar ratio has caused a more-polymerized silicate network via a net consumption of Q0, Q1, and Q2 species yet enriching in Q3 and Q4 species. Brillouin experiments revealed that all the bulk, shear and Young’s moduli of the glasses studied increases with the increase of CaO/P2O5 molar ratio. The unexpected variation trend in shear modulus can be correlated to the contribution from cohesion, the less-polymerized phosphate Q species, and density. Compared to the 45S5-derived, the more-polymerized 55S4-deived glass has a lower bulk but slightly higher shear modulus at the given CaO/P2O5 ratio.