Structure and properties of magnetite formed in the presence of nickel(II) ions

Fe3O4 particles prepared by oxidation of Fe(OH)2 precipitated from FeCl2 solutions containing different amounts of Ni2+ from 0 to 30 mol% were examined by various means. The thermogravimetry (TG) results show that the addition of Ni2+ raised the air-oxidation temperature of Fe3O4 particles from ca. 200 to ca. 400°C, which means that the Fe3O4 particles were stabilized to air-oxidation by the doped Ni2+. Fe2+ content of the materials obtained at Ni/(Ni + Fe) ≥ 0.1 mol% was significantly greater than the theoretical Fe2+ content of Fe3O4. Fe57 Mössbauer spectra indicated that Fe3+ ions in B sites of the Ni-doped Fe3O4 are exchanged in part by Fe2+. The dc electrical conductivity was increased from 10−4 to 10−2 S cm−1 by Ni2+ loading.