The Constitution of CuFe5O8

Abstract

The physical properties of the system CuFe₂O₄–Fe₃O₄ point to the existence of the compound CuFe₅O₈. The activation energies E_a of quenched specimens exhibit an anomaly at the composition CuFe₅O₈. The log of the resistivities plotted as a function of composition changes slope, the Curie temperatures T_c display a minimum, and the lattice constants A₀ show a maximum at or near this composition. As the iron concentration increases, the Seebeck coefficients θ change from positive to negative at the composition Cu_0.55(CuFe)_0.225Fe₂O₄. This is interpreted as being due to the introduction of some ferrous iron at this composition. The equilibrium Cu⁺¹+Fe⁺³↔Cu⁺²+Fe⁺² lies to the left at least up to this composition. Since the changes in ρ, E_a, A₀, and T_c occur at or near the composition CuFe₅O₈, it is concluded that only a little ferrous iron exists even in the region of n‐type conductivity, and that the copper within parentheses is predominantly monovalent in the series Cu_1−2x⁺²(Cu⁺¹Fe⁺³)_xFe₂O₄.