Isotopic disorder effect in the infrared reflection spectra of 6Lix7Li1−xY F4 single crystals

Polarized infrared reflection spectra of LiY F4 single crystals with different compositions of 7Li and 6Li isotopes were measured and analysed using the model of independent oscillators. Lattice dynamics calculations were performed. It was found that, for some modes, the contribution of the isotopic disorder to the damping constant is comparable to the anharmonic width. Results of simulations agree qualitatively with the experimental data. Possible reasons for the remaining discrepancies are discussed.