Temperature dependent magnetic structure of lithium delithiated Li_xFeSO_4F (x= 0,1) by Mossbauer spectroscopy

摘要

Recently, lithium iron sulfate compounds have been highly considered for a positive electrode material for lithium ion batteries. In this work, LiFeSO_4F and the fully delithiated FeSO_4F were prepared by the ionothermal process and chemical oxidation reaction method. The Li_xFeSO_4F (x = 0, 1) samples show the triclinic structure with P- space group. In the case of delithiated FeSO_4F, changes in lattice parameters were observed due to the disappearance of the Li site while maintaining the triclinic structure. Temperature-dependent magnetic susceptibility curves show the antiferromag-netic (AFM) structure with the ordering temperature of 28 K for LiFeSO_4F and 99 K for FeSO_4F. Also, temperature-dependent Mossbauer spectra of LiFeSO_4F below T_N were fitted with two-sets of eight Lorentzian indicating the existence of two different types of Fe~(2+) ions due to the different hyperfine and electric quadrupole interactions. With the lithium delithiated, the Fe~(3+) iron ions in FeSO_4F exhibit two-sets of six-line patterns due to the electron transfer in FeO_4F_2 site by lithium delithiation. These suggest that the different AFM ordering in Li_xFeSO_4F can be originated from the Fe~(2+)/Fe~(3+) magnetic ions with different charge distributions and spin contributions.