Physical and optical studies in mixed alkali borate glasses with three types of alkali ions

Abstract

So far only a handful of publications have been concerned with the study of the mixed alkali effect in borate glasses containing three types of alkali ions. In the present work, the mixed alkali effect (MAE) has been investigated in the glass system (40− x)Li 2O– xNa 2O–10K 2O–50B 2O 3. (0 ≤ x ≤ 40 mol%) through density and modulated DSC studies. The density and glass transition temperature of the present glasses varies non-linearly exhibiting mixed alkali effect. The glass stability is observed to be less which may be important for the present glasses as promising material for non-optical applications. We report, for the first time, the mixed alkali effect in the present glasses through optical properties. From the absorption edge studies, the values of indirect optical band gap ( E opt), direct optical band gap and Urbach energy (Δ E) have been evaluated. The values of E opt and Δ E show non-linear behavior with compositional parameter showing the mixed alkali effect. The average electronic polarizability of oxide ions α O 2 − , optical basicity Λ, and Yamashita–Kurosawa's interaction parameter A have been examined to check the correlations among them and bonding character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and interaction parameter, the present Li 2O–Na 2O–K 2O–B 2O 3 glasses are classified as normal ionic (basic) oxides.