Effect of CaO/MgO mixture on the structure and dielectric properties of alumino-borosilicate glass

Abstract

The rapid advancement and application of 5G/6G systems, has increased the demand for low dielectric glass fibers in high-frequency applications. However, challenges remain in optimizing their structure to improve the glass's thermal compatibility and performance at GHz frequencies. This study focused on SiO₂-Al₂O₃-B₂O₃-RO-TiO₂ alkali-free aluminosilicate glass and investigated the effect of mixed alkaline earth metals (CaO and MgO) on the glass structure. Furthermore, the relationship between the glass structure and its properties was analyzed. Several techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and magic-angle spinning nuclear magnetic resonance (MAS-NMR) were employed to conduct both qualitative and quantitative analyses the structure of glass. The study also evaluates the glass transition temperature, thermal expansion coefficient, high-frequency dielectric properties (ranging from 0.6 to 10 GHz), density, and chemical stability of this aluminosilicate glass. Experimental results indicate that when the CaO/MgO ratio is 1:4, the glass exhibits an optimal performance, achieving the lowest coefficient of thermal expansion (α =2.97 × 10⁻⁶ / °C) and the lowest dielectric constant (4.36 at 10 GHz). Both the FTIR and MAS-NMR results reveal that the introduction of mixed alkaline earth metals optimizes the tetrahedral network structure of this glass, leading to an enhanced performance. This study highlights the role of the alkaline earth metal mixing effect in adjusting the glass composition, providing valuable insights into the critical structure-property relationship of low-dielectric, low-expansion glass fibers and contributes to both high-frequency applications and practical production.