Concentration dependence of electric conductivity for fluorine-containing sodium borate glasses

Abstract

The influence of sodium fluoride additives on the physicochemical properties of glasses in the Na2O-B2O3 systems is investigated. The introduction of sodium fluoride into the Na2O · 2B2O3 and Na2O · 3B2O3 glasses leads to an increase in the electric conductivity. The temperature-concentration dependence of the electric conductivity has been investigated. It is shown that, in glasses of the NaF-Na2O · 2B2O3 system, an increase in the volume concentration of sodium ions from 2.4 × 10−2 to ∼3 × 10−2 mol/cm3 is accompanied by an insignificant decrease in the activation energy Eσ from 1.44 to 1.38 eV and a sharp (by a factor of ∼30) increase in the electric conductivity. In glasses of the NaF-Na2O · 3B2O3 system, an increase in the concentration of sodium ions from 1.8 × 10−2 to ∼2.3 × 10−2 mol/cm3 brings about an increase in the electric conductivity by a factor of approximately 100 and an increase in Eσ from 1.6 to 1.83 eV. A further increase in the concentration of sodium ions (up to 2.5 × 10−2 mol/cm3) virtually does not affect the electric conductivity and Eσ. At the same concentration of sodium ions (∼2.46 × 10−2 mol/cm3) in the 9.8NaF · 90.2[Na2O · 2B2O3] and 57.1NaF · 42.9[Na2O · 3B2O3] glasses, the electric conductivity and the activation energy are considerably higher in the glass with a larger fluorine content. The regularities revealed are interpreted in the framework of the microinhomogeneous glass structure.