Lattice Vibrations, Crystal Structure, Dielectric Properties, and Elastic Constants of AgF

The far-infrared transmission spectrum of AgF has been measured at room temperature and at 143°K in the region of the lattice vibrations. The zone-center transverse and longitudinal optic modes were found and their frequencies determined. The room-temperature crystal structure of AgF was restudied using x-ray diffraction, and an NaCl-type structure (Oh5) was confirmed with a lattice constant of 4.936±0.001 Å. Ellipsometry was utilized to determine the high-frequency refractive index of AgF; n=1.73±0.02. The static dielectric constant at room temperature (ε0=10.6±0.7) and at 143°K (ε0=10.3±0.3) was calculated using the Lyddane-Sachs-Teller relation. The Szigeti estimates of effective ionic charge and of compressibility were calculated, and their significance is discussed. Values were also computed for the elastic constants and the Debye characteristic temperature.