Manganese–Wüstite – (Fe1−x Mn x )1−δO

This Chapter discusses the diagrams of concentrations of defects in the oxide (Fe_1−x Mn _x )_1−δO with the manganese content of x _Mn = 0.037–1 mol/mol at 1173–1473 K based on the studies of the deviation from the stoichiometry. In the calculations, simple defects (cation vacancies [V^″ _M] [V^′ _M], [V^x _M]) and defect complexes {(V^″ _M)₂M^3• _i}′, {(V^″ _M)₄M^3• _i}^5′ and {(V^″ _M)₆(M^3• _i)₂}^6′ were taken into account. It was found that also in wüstite doped with manganese, in the range of low oxygen pressures, the so-called pseudo-phase w ₁ exists, and in the range of higher pressures, pseudo-phase w ₂. In the range of existence of the w ₁ and w ₂ pseudo-phase, cation vacancies [V^″ _M] dominate. Maximum concentration in the defect complexes is of an order of 0.01–0.001 mol/mol. The concentration of cation vacancies the coefficients of diffusion of defects were determined (mobility of iron ions via cation vacancies) at 1273 K with the use of the values of coefficients of iron diffusion in the oxides (Fe_1−x Mn _x )_1−δO obtained with the tracer method (⁵⁹Fe). The concentration of charge carriers and their mobility was calculated from the values of the electrical conductivity in the oxides (Fe_1−x Mn _x )_1−δO. It was shown that the character of the dependence of electrical conductivity on the oxygen pressure is strictly dependent on the concentration of ions [M³⁺]. Above 1400 K, there occurs a change in the transport mechanism (there occurs a semiconductor/metal transition). It was shown that similarly as in the manganese oxide, also in the oxides (Fe_1−x Mn _x )_1−δO with the manganese content of x _Mn = 0.6–1.0 mol/mol the mobility of electrons is much higher than the mobility of electron holes.