Temperature dependence of refractive index and electronic polarizability of KNbGeO5 glass and its nanocrystallized glasses

Abstract

The refractive indices (n) and densities (ρ) of a glass and transparent nanocrystallized glasses with the composition of 25K2O-25Nb2O5–50GeO2 (i.e., KNbGeO5) are measured in the temperature range of 30–150 °C in order to clarify the temperature dependences 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, and the values of the temperature dependence of these properties, i.e., dn/dT, dαO2−/dT, and dΛ/dT, tend to decrease slightly due to the nanocrystallization. It is clarified that the temperature dependence of the electronic polarizability of oxide ions in the precursor glass and nanocrystallized glasses has a large contribution for the temperature dependence of the refractive index in comparison with the contribution of density (volume thermal expansion). The features in the temperature dependences of αO2− and Λ in the present glass system is related to the large optical basicities of the constituent oxides of K2O, Nb2O5, and GeO2.