Temperature coefficient of electronic polarizability in optical glasses

The temperature coefficient of refractive index dn/dT and that of volume expansion β have been measured by an interferometric procedure designed to determine the coefficients simultaneously, with one sample. The temperature coefficient of electronic polarizability φ have been calculated from dn/dT and β. φ is expressed as the sum of the contributions of each glass component, φ_i·φ_i is expressed as follows: φ_i = ß_iγ_i, where ß_i is the thermal change in cation-oxygen distance and γ_i is the change in electronic polarizability due to the inter-ionic distance change. φ_i decreases as the ionic field strength z/a² of the cation increases, which is the same tendency as that of ß_i. γ_i, calculated from φ_i and ß_i, gradually increases as z/a² increases. This means that φ_i is mainly determined by the elongation of the inter-ionic distance, and it also suggests that the deformation of the electron cloud of oxygen ion due to the inter-ionic distance change, γ_i becomes larger, as the electronic polarizing power of the cation increases.