Optical dispersion studies ofβ−LiAl

The room-temperature reflectance spectra of several compositions of LiAl within the $\beta$ phase have been measured from 33 to 50000 ${\mathrm{cm}}^{-1\mathrm{}}$. The spectra were found to exhibit plasmon-type behavior and were analyzed by a multiple-plasmon model for the dielectric permittivity. This analysis indicated a significant decrease in the static electrical conductivity when going from Li-deficient to Li-rich compositions. It was also concluded that the conductivity was primarily determined by the properties of a single underdamped plasmon mode in which both the plasma frequency and scattering time showed a strong dependence upon Li concentration. The results are discussed in view of recent theoretical calculations.