Structure-terahertz property relationship in sodium borosilicate glasses

Abstract

We report, for the first time, an early evidence of structure-terahertz (THz) property relationship for two tie-lines within the sodium borosilicate glass system. The NaBSi series was chosen to study the effect of the substitution of silicon dioxide for boron oxide, whereas the BNaSi series studies the substitution of silicon dioxide for sodium oxide. Nuclear magnetic resonance, infrared absorption, and Raman spectroscopies were used to determine structural changes across both series. THz time-domain spectroscopy was used to record the refractive index over the measured bandwidth. Individual measurements at .502 THz were used as a frequency of focus for comparisons. The foundation for the proposed structure-THz property relationship is based on higher measurable THz refractive index changes correlated to a depolymerized glass network, R > .5, a network consisting of SiO₄ tetrahedra and charge-deficient [BØ₄]⁻ tetrahedra-forming borosilicate danburite and reedmergnerite rings with mixed Si–O–B bridges, and the formation of nonbridging oxygen (nbO) atoms on silicate tetrahedra. A polymerized glass network, R < .5, consists of homonuclear boroxol and silica rings within sodium borate and silicate subnetworks. Calculated and experimental fractions of tetrahedral borate and silicate tetrahedra with one nbO, optical basicity, density, and network connectivity data support the structure-THz property relationship.