Thermo‐Optic Properties and Electronic Polarizability in Alkali Tellurite Glasses

Abstract

The refractive indices (n) and densities (ρ) of xLi2O–(100−x)TeO2 glasses with x=15–30 and xNa2O–(100−x)TeO2 glasses with x=10–20 are measured in the temperature range of 30°–150°C in order to clarify thermo‐optic coefficients (dn/dT) and the temperature dependence of the electronic polarizability of oxide ions ( ) and optical basicity (Λ). It is found that the values of n, , and Λ increase almost linearly with increasing temperature. The values of dn/dT are around 7 × 10−5 K−1 and tend to decrease with increasing alkali content (Li2O, Na2O). In contrast, the values of d/dT and dΛ/dT are almost constant, irrespective of the alkali content. It is suggested that electronic polarizability has an important contribution on thermo‐optic coefficients, but the contribution of volume thermal expansion on thermo‐optic coefficients cannot be ignored. In the analyses of electronic polarizabilities of alkali tellurite glasses, the concept of group optical basicity for TeO3 and TeO4 structural units is also applied. It is explained that large thermo‐optic coefficients in Li2O–TeO2 and Na2O–TeO2 glasses are composed of oxides having small average single bond strengths and large optical basicities.