Effect of Composition and Thermal History on Dielectric Constants of Soda‐borosilicate Glasses*

A bstract The dielectric constants, densities, and refractive indices of two series of soda‐boro‐silicate glasses were measured at 25° C. on some quenched specimens and on other specimens that were stabilized at different temperatures. The compositions of the two series were Na 2 O‐4.69 SiO 2 ‐B 2 O, (0 to 45%) and Na 2 O B 2 O 3 ‐SiO 2 (30 to 100%), respectively. The structure of the glasses was found to depend on the ratio of oxygen atoms to the sum of the boron and silicon atoms and also on the concentration of the sodium ions. If the ratio of O to B + Si is greater than 2.0 or if the ratio of oxygen to sodium ions is less than 6.0, some of the oxygens are bonded only to one boron or to one silicon atom. The presence of “single‐bonded” oxygen atoms in the glass structure leads to a lower density and a higher dielectric constant and refractive index. The dielectric constant decreases and the density increases continuously as the temperature of heat treatment is lowered. The effect of heat treatment is greater for the glasses which contain the larger number of “single‐bonded” oxygen atoms and the higher concentration of sodium ions.