Temperature dependence of refractive index and electronic polarizability of RO–TeO2 glasses (R=Mg, Ba, Zn)

Abstract

The refractive indices (n) and densities (ρ) of xRO − (100 − x)TeO2 glasses (R = Mg, Ba, and Zn) with x = 10–40 are measured in the temperature range of 50–150 °C in order to clarify thermo-optic coefficients (dn/dT) and the temperature dependence of the electronic polarizability of oxide ions (αO2−) and optical basicity (Λ). It is found that the values of n, αO2−, and Λ increase almost linearly with increasing temperature. The values of dn/dT are between 7.32 and 9.69 × 10−5 K−1 and tend to decrease with increasing RO content. Contrary, the values of ⅆαO2−/ⅆT and dΛ/dT are almost constant irrespective of RO content. It is suggested that the electronic polarizability has an important contribution on thermo-optic coefficients, but the contribution of volume thermal expansion on thermo-optic coefficients is not ignored. In the analyses of electronic polarizabilities of RO–TeO2 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 RO–TeO2 glasses are composed of oxides having small average single bond strengths and large optical basicities.