ИСТИНА

In this work we study the effect of doping on local states of iron atoms and hyperfine interactions of 57Fe nuclei and also on changes that takes place during the electrochemical charging. The charging process implies lithium ions extraction. Mössbauer spectra of LixFe1-yMyPO4 (M = Mg, Mn, Co, Ni, Zn; 0 ≤ y ≤ 0.3) were collected at temperatures above and below the temperature of magnetic ordering. All the spectra were fitted using the SpectrRelax program. Spectra at 300 K can be fitted by set of quadrupole doublets. Both the reconstruction of the hyperfine field distribution and the model fitting within framework of the Hamilton model were used to process spectra at 5.5 K. Some spectra collected at intermediate temperatures need to be fitted using the relaxation models. Substitution of Fe cations noticeably affects hyperfine parameters of Fe3+ subspectra in the Mössbauer spectra of studied materials exposed to different degree of charging. At the same time the influence on Fe2+ subspectra is less pronounced but it still can be detected. The oxidation of Fe2+ cations to the trivalent state during the charging was observed for all studied samples. Doping can prominently influence on charging process. As for samples doped with Mn further increase of charging voltage leads to oxidation of Mn2+ cations too. Doping with Mg results in formation of nanoscale regions containing Fe3+ cations at the intermediate stages of the charging process. Distribution of dopant cations over Fe positions depends on the type of dopant (it is not always statistical), for instance Co cations are orderly distributed, so each Fe cation has no more than one Co2+ cation in the nearest environment.