Phonon calculation on olivine-like LiMPO4 (M = Ni, Co, Fe) and Raman scattering of the iron-containing compound

The phonon properties of the lithium transition metal phosphates LiMPO4 (M = Ni, Co, Fe) with the olivine structure were studied using a computational simulation. The calculation employs a normal coordinate analysis based on the Wilson's FG matrix method. The method applied to LiNiPO4 allowed for the fitting of a set of stretching force constants and angle bond strengths that resulted in Raman wavenumbers comparing with experiments within a 5% average deviation. This set was assumed fixed for the isostructural Co‐containing and Fe‐containing compounds, as a first approximation. The calculated LiCoPO4 Raman wavenumbers also compared well with experimental values (average deviation 9%). Using this procedure, the 36 Raman wavenumbers of LiFePO4 were predicted and assigned to vibrational motions and symmetry species of the crystal group. LiFePO4 unpolarized Raman data agree very well with the predicted values. Copyright © 2004 John Wiley & Sons, Ltd.