Role of F− ions in the structure and properties of BaF2B2O3 glasses

Abstract XRD, TEM, SEM, FTIR and NMR spectroscopies have been used to explore the role of F− ions in structure of BaF2 B2O3 glasses. Up to BaF2 ≈ 35 mol% the majority of fluorine enters the glass network to convert BO3 units into Ba 1 / 2 2 + BO 3 F − (B4 units) with B F linkages. For BaF2 > 35 mol%, a part of BaF2 forms its own matrix in the form of amorphous and crystalline phase, built of BaF4 tetrahedra. Calculated N4 values from IR spectra agree well with the data obtained from NMR spectroscopy. SEM shows clusters of different size separated from the amorphous phase. Changes in Tg reveal that the B F bonds are weaker than B O bonds. Density and molar volume calculated on the basis of the presented model are in excellent agreement with the experimental data. Abrupt changes in conductivity and activation energy for BaF2 > 35 mol% are correlated with the presence of BaF4 clusters and changes in free volume and packing density. As far the authors know, BaF2 B2O3 glasses are investigated for the first time.