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

The refractive indices (n) and densities (rho) of a glass and transparent nanocrystallized glasses with the composition of 25K(2)O-25Nb(2)O(5)-50GeO(2) (i.e., KNbGeO5) are measured in the temperature range of 30-150 degrees C in order to clarify the temperature dependences of the electronic polarizability of oxide ions (alpha(O2-)) and optical basicity (Lambda). It is found that the values of n, alpha(O2-), and Lambda increase almost linearly with increasing temperature, and the values of the temperature dependence of these properties, i.e., dn/dT, d alpha(O2-)/dT, and d Lambda/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 alpha(O2-) and Lambda in the present glass system is related to the large optical basicities of the constituent oxides of K2O, Nb2O5, and GeO2.