Effect of mutual modification by BaO and BaF2 on the structure and properties of BaO–BaF2–B2O3 glasses.

Oxy-fluoroborate glasses of the composition xBaF₂·(45-x)BaO·55B₂O₃ (0 ≤ x ≤ 45 mol%) have been prepared by the normal melt-quenching technique. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the glassy matrix contains amorphous and/or crystalline phases depending on BaF₂ concentration. Scanning electron microscopy (SEM) shows agglomerates consisting of clusters in micro-scale separated from the amorphous phase. Fourier-transform infrared (FTIR) spectra reveal that BaF₂ partially modifies the borate matrix as in the binary BaF₂–B₂O₃ glasses. Values of fraction N₄ of four coordinated boron atoms calculated from FTIR spectra agree with nuclear magneitic resonance (NMR) data. N₄ increases at the expense of non-bridging planar trigonal (BO₃) units at low concentrations of BaF₂ while at higher concentrations, N₄ increases at the expense of tetrahedral BO₄ units. Density seems to be constant while molar volume increases from 27.51 to 30.31 cm⁻¹ with increasing BaF₂ content. It is found that the volume of structural units by BaF₂ is greater than those related to BaO. T_g have a linear decrease from 580 to 485 °C with increasing BaF₂ concentration. A structural view is presented for the role of BaF₂, obtained based on N₄ data obtained from NMR and FTIR analysis. [ABSTRACT FROM AUTHOR]