FTIR, Raman and NMR investigation of CaO–SiO2–P2O5 and CaO–SiO2–TiO2–P2O5 glasses

• The structure of CaO–SiO2–P2O5 and CaO–SiO2–TiO2–P2O5 glasses was identified.
• FTIR, Raman and 31P MAS NMR spectra were obtained and analyzed.
• P2O5 addition increased the degree of polymerization (DOP) of the glasses.
• Phosphorous mainly existed as isolated Q0(P) and terminal Q1(P) in the glasses.
• The mole ratio of Q0(P) to Q1(P) decreased with increasing P2O5 content.

The role of P2O5 on the structure of CaO–SiO2–P2O5 and CaO–SiO2–TiO2–P2O5 glasses was identified using Fourier transformation infrared (FTIR), Raman and Magic Angular Spinning Nuclear Magnetic Resonance (MAS NMR) spectra in this study to provide some fundamental clues for titanium and phosphorus extraction. In both systems, the vibration signals of Q0(Si), Q1(Si), Q2(Si), and Q3(Si) were detected and the dominant structural units associated with P–O groups were isolated Q0(P) and terminal Q1(P) (Qi(Si,P), i represents the number of bridging oxygen per Si or P). The added P2O5 resulted in an increase of Q3(Si) at the cost of Q0(Si), Q1(Si), and Q2(Si) and the degree of polymerization (DOP) of the glasses was therefore increased; additionally, the mole ratio of Q0(P) to Q1(P) decreased with increasing P2O5 content, indicating an equilibrium reaction between Q0(P) and Q1(P). Furthermore, the presence of TiO2 resulted in a more complicated structure in the CaO–SiO2–TiO2–P2O5 glasses and the structural units related to Q0(P), O–Ti–O deformation and TiO44 − monomers were clearly clarified.