Magnetite Doped with Manganese and Cobalt – (Co x Mn z Fe2z )3±δO4

The chapter presents the diagrams of defects’ concentrations for the spinel (Co x Mn z Fe 2 z ) 3±δ O 4 with the cobalt content of x Co = 0.1–0.333 mol at 1473 K based on the deviation from the stoichiometry data. In the range of higher oxygen pressures cation vacancies [V ‴ Fe ] dominate, and the character of the dependence of their concentration on the oxygen pressure is analogous to the case of pure magnetite and the spinel MnFe 2 O 4 (exponent about 2/3). When the cobalt content in (Co x Mn z Fe 2 z ) 3±δ O 4 increases, the concentration of cation vacancies significantly decreases (at the same oxygen pressure). In the range of low oxygen pressures, interstitial cations [ Fe 3• i ] dominate. The ratio of the coefficient of diffusion (mobility) of tracer ions via interstitial cations to the coefficient of diffusion via vacancies ( D o I(M) / D o V(M) = b D ) in the spinel (Co x Mn z Fe 2 z ) 3±δ O 4 was calculated based on the concentration of ionic defects and the values of coefficients of self-diffusion of tracers M* ( 59 Fe, 60 Co and 53 Mn). It was found that when the cobalt content in the spinel (Co x Mn z Fe 2 z ) 3±δ O 4 increases, the mobility of tracer ions via interstitial cations is higher than the mobility via cation vacancies and at the cobalt content of x Co = 0.1 mol the parameter b D reaches the highest values. At 1473 K, the values of the parameter b D for cobalt ions is b D ≈ 95, for manganese b D ≈ 31, and for iron ions b D ≈ 16.