Thermodynamic model and Raman spectra of binary barium borate glassforming melts

The set of 34 baseline subtracted and thermally corrected Raman spectra of BaO–B2O3 glassforming melts with the composition xgBaO–(1 − xg)B2O3 (xg = 0.20; 0.25; 0.30; 0.35; 0.40; 045; 0.50; 0.55; 0.60) measured at temperatures ranging from 600 to 1100 °C was analyzed. The thermodynamic model of Shakhmatkin and Vedishcheva was evaluated for each glass melt. Nine following system components (defined as stable crystalline phases of the BaO–B2O3 binary phase diagram) were considered: BaO, B2O3, 2BaO·5B2O3 (Ba2B5), 2BaO·B2O3 (Ba2B), 3BaO·B2O3 (Ba3B), 4BaO·B2O3 (Ba4B), BaO·B2O3 (BaB), BaO·2B2O3 (BaB2), and BaO·4B2O3 (BaB4). The equilibrium molar amounts of system components were used for the evaluation of the molar amounts of basic structural units Tn (trigonal boron with n-bridging oxygen atoms, n = 0, 1, 2, 3) and Q4 (tetragonal boron with 4-bridging oxygen atoms). Only three structural units (Q4, T3, and T2) with the not negligible equilibrium molar amount were found. The significant correlation between equilibrium molar amounts of Q4 and T3 was found. Malfait’s decomposition was performed for the most abundant units, i.e., T3 and T2. Multivariate curve resolution analysis performed for two components resulted in the Raman spectra (so-called loadings) and relative abundances (so-called scores) of each component. The obtained loadings were in good agreement with the partial Raman spectra obtained by the Malfait’s decomposition.