Sol-gel preparation and high-energy XRD study of (CaO)(x)(TiO2)(0.5-x)(P2O5)(0.5) glasses (x=0 and 0.25)

Glasses from the CaO-TiO2-P2O5 system have potential use in biomedical applications. Here a method for the sol-gel synthesis of the ternary glass (CaO)(0.25)(TiO2)(0.25)(P2O5)(0.5) has been developed. The structures of the dried gel and heat-treated glass were studied using high-energy X-ray diffraction. The structure of the binary (TiO2)(0.5)(P2O5)(0.5) sol-gel was studied for comparison. The results reveal that the heat-treated (CaO)(0.25)(TiO2)(0.25)(P2O5)(0.5) glass has a structure based on chains and rings of PO4 tetrahedra, held together by a combination of electrostatic interaction with Ca2+ ions and by corner-sharing oxygen atoms with TiO6 octahedra. In contrast, the (TiO2)(0.5)(P2O5)(0.5) glass has a structure based on isolated P2O7 units linked together by corner-sharing with TiO6 groups. The results suggest that both the dried gels possess open porous structures. For the (CaO)(0.25)(TiO2)(0.25)(P2O5)(0.5) sample there is a significant increase in Ca-O coordination number with heat treatment.