Cobalt-Doped Magnetite – (Fe1−x Co x )3±δO4

This chapter presents the diagrams of the concentrations of defects for the spinel (Fe_1−x Co _x )_3±δO₄ with the cobalt content of x _Co = 0.1–0.333 mol, for the temperature of 1473 K based on the deviation from the stoichiometry data. In the range of higher oxygen pressures, cation vacancies [V^‴ _Fe ] dominate, and in the range of low oxygen pressures, interstitial cations [Fe ^3• _i] dominate. The above character of the dependence of δ on p _O2 is an effect of the incorporation of Co²⁺ ions into the spinel structure, into the sublattice of Fe³⁺ ions that are negative in relation to the lattice (Co ^′ _Fe). The concentration of these ions increases with the cobalt content in the spinel, and at the content of x _Co= 0.2 mol reaches the value of y _Co = 0.0014 mol/mol, and then at the content of x _Co= 0.333 mol it decreases to zero. The ratio of the coefficient of diffusion (mobility) of tracer ions via interstitial cations to the coefficient of diffusion via cation vacancies (D ^o _I(M)/D ^o _V(M) = b_D ) was calculated from the concentration of ionic defects and the values of coefficients of self-diffusion of tracers M* (⁵⁹Fe, ⁶⁰Co and ⁵³Mn). It was found that when the cobalt content in the spinel (Fe_1−x Co _x )_3±δO₄ increases, the mobility of ions via interstitial cations is higher than the mobility via cation vacancies and at the cobalt content of x _Co = 0.333 mol the parameter b _D reaches the highest values.