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Lithium deintercalation of (1-x) LiFePO4/x FePO4(0 les x les 1) have been studied with X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), and Mossbauer spectroscopy. Lithium deintercalation to obtain (1-x) LiFePO 4/x FePO 4 was done by chemical oxidation process using NO2 BF4 . The crystal structure was found to be an orthorhombic with space group Pnma for each sample. There exists a mixture of LiFePO4 and FePO4 phase between x = 0 and 1 . The Mossbauer spectra have been taken at various temperatures ranging from 4.2 K to room temperature. The magnetic Neel temperature (TN) was determined to be 51 and 114 K for LiFePO4 and FePO4 . Also, the iron ions were ferric and ferrous for LiFePO4 and FePO4, both occupying the octahedral sites at various temperatures. We confirmed that the change of Mossbauer spectrum shape as the evidence of two-valence state of iron ions coexists on lithium deintercalation in LiFePO4 from 4.2 K to room temperature.
Date of Publication: Oct. 2009