Glass transition temperatures and structures of multicomponent borate glasses: Influence of modifier cation field strengths

• Published in: Journal of non-crystalline solids Vol. 438; pp. 1 - 6
• Main Authors: Vassilev, Tsvetan, Penkov, Ivan, Tzvetkova, Christina, Pascova, Radost
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2016
• Subjects: Borate glasses; Borates; Cations; Depolymerization; DSC; Field strength; Glass; Glass structure; Glass transition temperature; Infrared spectroscopy; Networks; Oxides; Borate glasses; Infrared spectroscopy; Glass structure; DSC; Glass transition temperature
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2016.02.007

Glass transition temperatures, Tg, are determined for a series of multicomponent borate glasses with composition xPbO·(33.33−x)Na2O·yAl2O3·1.3ySiO2·(66.67−2.3y)B2O3, (where x and y take values from 0 up to 13.5mol%, and from 0 up to 5.3mol%, respectively). For this purpose, differential scanning calorimetry is used while the structure of these glasses containing two kinds of modifier oxides — Na2O and PbO, is investigated by infrared spectroscopy. A detailed analysis of the infrared spectra reveals that at constant total content of the glass-forming oxides (B2O3, SiO2 and Al2O3) in the glasses investigated, the borate network progressively depolymerizes when Na2O is substituted for PbO. This substitution favors the destruction of the more rigid structural units and the formation at their expense of units with a lower degree of connectivity. The macroscopic manifestation of these structural changes is the steep decrease in the glass transition temperature of the glasses investigated at increasing PbO concentration. This tendency for depolymerization of the borate network is explained by the influence of the Pb2+-cations possessing substantially higher ionic field strength as compared to that of the Na+-cations. •The influence of PbO on the Na2O-B2O3-SiO2-Al2O3 glass system is investigated.•The glass transition temperature Tg decreases when Na2O is substituted for PbO.•IR studies reveal that this substitution leads to depolymerization of the borate network.•The higher field strength of the Pb2+ cations as compared to the Na+ cations is the main reason for this depolymerization.