The Structural Transition and Magnetic Properties of Lithium Deintercalation in LiFePO $_{4}$

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.