Raman Spectroscopy of $LiFePO_4$ and $Li_3V_2(PO_4)_3$ Prepared as Cathode Materials

Structure of samples of lithium iron vanadium phosphates of different compositions were investigated by X-rays, electron microscopy and Raman spectroscopy. The investigated salts were mainly of olivine-like and NASICON-like structures. The X-ray diffraction and the Raman scattering show different crystalline structures, which is probably caused by difference between cores of the crystallites (probed by X-rays) and their shells (probed by the Raman scattering). Most of the Raman spectra were identified with previously published data, however in the samples with high vanadium concentration we have observed new, not reported earlier modes at 835 $cm^{-1}$ and 877 $cm^{-1}$, that we identified as oscillations related to $V_2O_7^{4-}$ or $VO_4^{3-}$ anions.