IR Active Phonons of a LiNiPO4 Ionic Crystal

The results of an experimental study of the phonon spectrum of a LiNiPO4 single crystal by infrared (IR) reflection spectroscopy are presented. Spectroscopic parameters of phonons active in IR spectra are obtained. The observed number of phonons is generally in agreement with the performed group-theoretical analysis. The reasons for small discrepancies are discussed. With decreasing temperature, a hardening of phonon frequencies is observed, which is associated with temperature changes in the parameters of the crystal lattice.