Manganese-Doped Magnetite – (Fe1−xMn x )3±δO4

This chapter presents the diagrams of the concentrations of defects in the spinel (Fe_1−x Mn _x )_3±δO₄ with the manganese content x _Mn= 0.1–0.4 mol at 1473 K based on the deviation from the stoichiometry data. It was found that the range of existence of spinel (Fe_1−x Mn _x )_3±δO₄ shifts towards higher oxygen pressures when the manganese content increases. Manganese doping of spinel (Fe_1−x Mn _x )_3±δO₄ does not practically affect the point defects structure. At higher oxygen pressures, cation vacancies [V^‴ _Fe ] dominate, and in a range of low oxygen pressures, interstitial cations [Fe ^3• _i] dominate. When the manganese content in the spinel (Fe_1−x Mn _x )_3±δO₄ increases, standard Gibbs energy of formation of Frenkel defects increases, which results in a decrease in the concentration of Frenkel defects from the value of 1.5⋅10⁻⁴ to 3⋅10⁻⁵ mol/mol. The ratio of the coefficients of diffusion (mobility) of iron ions via interstitial cations to the coefficient of diffusion via vacancies (D ^o _I(Fe)/D ^o _V(Fe) = b _D) was determined based on the concentration of ionic defects and the values of coefficients of self-diffusion of iron ions ⁵⁹Fe. It was found that at the manganese content x _Mn= 0.2–0.3 mol in the spinel (Fe_1−x Mn _x )_3±δO₄, the mobility via interstitial cations is higher than the mobility via cation vacancies and their ratio reaches the value of b _D ≈ 12 and then it decreases.