Computational and spectroscopic comparative analysis of Raman phonon spectra of LiNiPO₄.

This article focuses on the Raman spectroscopic investigation of a lithium orthophosphate single crystal, LiNiPO4, across its magnetic phase transition near 21.9 K. The study identifies shifts in specific phonon modes associated with both external vibrations and internal vibrations of the (PO4)3– tetrahedra, which are attributed to significant spin-phonon coupling and magnetostriction effects influencing the crystal lattice during the transition to a magnetically ordered state. Using shell-model lattice dynamical calculations, the observed phonon modes were assigned to their symmetries, showing reasonable agreement with experimental data. The findings highlight the selective impact of magnetostriction on ionic bonds in LiNiPO4 and contribute to understanding the coupling between magnetic and lattice subsystems in this material.