Evolution of lattice defects in nickel ferrite spinel: Oxygen vacancy and cation substitution

Oxygen deficiency is a common phenomenon in the sintering process of nickel ferrite spinel, and has a significant impact on the properties of the NiFe2O4 sintered body. This work investigated the effects of oxygen deficiency on the evolution of the lattice defects in spinel crystal. The oxygen deficiency led to the generation of a non-stoichiometric nickel ferrite containing oxygen vacancies (NiFe2O4-δ). As the sintering temperature increased from 1150 °C to 1400 °C, the concentration of oxygen vacancies in NiFe2O4-δ increased, with a δ value increasing from 0.0014 to 0.0355 and a lattice parameter increasing from 8.3485 to 8.3567 Å. X-ray photoelectron (XPS), Fourier transform infrared (FTIR) and Raman spectroscopy all showed that the crystal structure of NiFe2O4-δ belonged to the Fd3m space group with Fe2+ ions partially replacing Fe3+ in the octahedral sites. Furthermore, a tendency for NiFe2O4-δ to decompose to Ni alloy and Fe3O4 during sintering could be observed.