Synergistic thermo-Raman and calorimetric kinetic study of the cation modifier's role in binary metaphosphate glasses

A comprehensive temperature-dependent Raman spectroscopy and differential scanning calorimetry study has been performed on three metaphosphate glasses with different modifying cations (Ca²⁺, Ba²⁺, and Pb²⁺). The P–NBO (nonbridging oxygen) Raman spectral feature, the force constant, and the glass transition activation energy (AE_Tg) are shown to be strongly correlated to the relative effective nuclear charge difference between the modifying and the glass former cations, ζ. In addition, the estimated AE_Tg values between 3.6(2) and 4.7(2) eV are found to be in the range of the P–O bond energy values in the phosphate glasses. The study contributes to the enrichment of the bond exchange kinetic theory of the glass transition in general and to the bond modifying mechanism of the cations. The authors propose that Raman spectroscopy alone can be implemented reliably for evaluation not only of AE_Tg, but for calculation of the Morse potential of the moiety crucial for the onset of glass transition. Alternatively, in glasses without Raman scattering, the force constant of the critical moiety can be deduced from calorimetric measurements alone. The proposed analytical methodology broadens Raman spectroscopy and calorimetric applications and offers a viable technique for all types of glass matrices.