Vibrational spectroscopic investigation of structurally-related LiFePO4, NaFePO4, and FePO4 compounds.
Vibrational spectroscopy was utilized to investigate the local structure of LiFePO(4), NaFePO(4), and FePO(4). The factor group splitting of the intramolecular PO(4)(3-) vibrations is between 10 and 20 cm(-1) less for NaFePO(4) than for LiFePO(4). This is because Li(+) ions have a higher charge density than Na(+) ions and can form stronger coordinative bonds with the PO(4)(3-) anions. Thus, the internal modes are more perturbed in LiFePO(4) and exhibit larger factor group splitting effects. The similarity of the factor group multiplets for both LiFePO(4) and NaFePO(4), particularly the PO(4)(3-) bending modes, strongly suggests that the 506 and 470 cm(-1) bands of LiFePO(4) consist almost entirely of lithium translatory motion. There are marked differences between the vibrational spectrum of FePO(4) and those of LiMPO(4) (M=Mn, Fe, Co, or Ni) or NaFePO(4). The monovalent cations interact with the oxygen atoms of the phosphate groups, affecting the frequencies and intensities of the intramolecular PO(4)(3-) modes, in a manner that is absent in FePO(4).
Burba
Christopher M
CM
Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Room 208, Norman, 73019, USA.
Frech
Roger
R
D004563:Electrochemistry; D005290:Ferric Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman / Q000379:methods*
D005290:Ferric Compounds; C473349:LiFePO4; D010710:Phosphates; D008094:Lithium; D007501:Iron