Lattice spectrum and dielectric properties of EuF₂

Abstract

Measurements at room temperature of the infrared reflectivity, low frequency dielectric constant (ε{lunate}g = 7.7 ± 0.2) and optical index of refraction (n = 1.555 ± 0.005) have been carried out on EuF2. The data have been analyzed both by classical dispersion theory and Kramers-Kronig relations to obtain the frequency dependent dielectric dispersion from 50 cm-1 to 1400 cm-1. As has been found for other crystals of the fluorite type, a single strong resonant absorption is found. The optical mode frequencies are ωt0 = 194 cm-1; ωl0 = 347 cm-1. The best classical dispersion formula fit to the reflectivity yields the following parameters: ω0 = 195.2 cm-1, 4πρ = 5.15, \ ̄gg = 25.2 cm-1. The (Szigeti) effective charge on the Eu+2 ion is 1.67 e. These results are used to discuss polarizabilities, covalency, and crystal chemistry of divalent europium compounds within the context of a 'shell' model. © 1966.