Local Density Information From Low Energy-Loss Peels Measurements

It is known that radiation produces microscopic and macroscopic changes in silicas and other silicate glasses that result in densifications of several percent [1], This change in density is matched by a corresponding linear change in refractive index via the Lorentz-Lorenz relation such that where R is the molar polarizablilty, V the molar volume and n the refractive index.- Measurements of neutron irradiated bulk a-Si02 yield an exact correlation between the refractive index and density as shown by Fig. 1 such that dn/dp =185 m3/kg [ 1 ].Utilizing a VG HB603 STEM fitted with a parallel EELS, measurement of irradiation-induced density changes in silicas were attempted using the 0-100 eV low-loss region of the electron energy-loss spectrum. The dielectric function and refractive index changes were extracted from these data using a modified Kramers-Kronig analysis (Fig. 2).

Analysis of Thermal Variation of Length and Refractive Index of Lead Fluoride to Study its Optical Properties

Linear thermal expansion and refractive index variation have been measured in lead fluoride with a laser interferometer as a function of temperature. Data has been analyzed using the Lorentz-Lorenz relation. Molecular polarizability, band gap, variation of refractive index with density, and strain-polarizability parameter have been studied as a function of temperature. They exhibit a small variation with temperature except near the superionic phase transition where the variation appears to be more pronounced. The results are in good agreement with the published data near room temperature.