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

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−αO2−) and optical basicity (Λ). It is found that the values of n  , αO2−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−/ⅆTⅆαO2−/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.

Graphical abstractThis figure shows the temperature dependence of refractive indices (n) (i.e., thermo-optic coefficient) for xZnO − (100 − x)TeO2 glasses in the temperature range of 30–150 °C. The temperature dependence of refractive index is a very important physical property in the solid state science, and it is possible to evaluate the temperature dependence of electronic polarizability.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Refractive indices and densities of MgO–, BaO–, ZnO–TeO2 glasses were measured in the range of 30–150 °C. ► Glasses showed large temperature dependences of electronic polarizability of oxide ions and optical basicity. ► Large thermo-optic coefficients are a common feature of TeO2 oxide. ► Structure groups of TeO4−, TeO4o, and TeO3− have similar temperature dependences of optical basicity.