Crystallization and stoichiometry of crystals in Na2CaSi2O6–P2O5 based bioactive glasses

Devitrification treatment of Na2CaSi2O6–P2O5 based bioglasses (45S5.2 and 55S4.1) at 715 °C for up to 90 min caused amorphous phase separation via a bulk nucleation and growth mechanism, and then the formation of a single crystalline phase from the dispersed phosphorus-rich amorphous phase. The combined evidences of X-ray diffraction, optical/electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy and density measurement indicated the crystal is approximately hexagonal in symmetry. Based on the isochemical crystallization of this phase from the 45S5.2 glass and the chemistry/density considerations, we suggested that the crystal is non-stoichiometric (Na0.951Ca0.049)2Ca(Si0.899P0.101)2O6. The 55S4.1 glass was partially crystallized as the same phase with relic SiO2-rich glass. The 45S5.2- or 55S4.1-based glass ceramics with tailored size and distribution of Na2CaSi2O6-type crystal may have potential applications as clinical implants.