An effect of scandium substitution on the phase purity and structural, magnetic, and electrochemical features of ε-Fe ₂ O ₃ nanoparticle systems

A series of Sc-substituted ε-Fe₂O₃ nanoparticles embedded in a silica matrix were synthesized by a sol-gel process. It was found that the preparation of a pure ε-Fe₂O₃ phase without any other iron(III) oxide phases as admixtures was achieved for ε-Sc_0.1Fe_1.9O₃ (5 at% of Sc) as documented by analyses of X-ray powder diffraction (XRD) results. Extensive physicochemical characterization of the ε-Sc_0.1Fe_1.9O₃ sample was performed employing transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), magnetization measurements, ⁵⁷Fe Mössbauer spectroscopy, and electrochemical impedance spectroscopy (EIS). Magnetization vs. temperature plots showed vanishing of the two-step magnetic transition for the Sc-doped ε-Fe₂O₃ sample; a decrease in the magnetization profile was observed only once upon the change in the temperature. The Sc³⁺ substitution was found to cause a constriction of the magnetic transition region and a shift of the onset of the magnetic transition to a higher temperature in comparison with the undoped ε-Fe₂O₃ system. Moreover, upon the introduction of Sc³⁺ ions in the ε-Fe₂O₃ crystal lattice, a magnetic hardness was altered accompanied by a decrease in the coercivity. With ⁵⁷Fe Mössbauer spectroscopy, it was identified that Sc³⁺ predominantly substitutes Fe³⁺ in the distorted octahedral A- and B-sites and with almost equivalent occupation probability at both positions. Moreover, the electrochemical measurements confirmed the increase in the resistivity in the Sc-doped ε-Fe₂O₃ systems. Thus, the results, achieved within the present study, demonstrated an effect of Sc³⁺ substitution on the preparation purity of ε-Fe₂O₃ systems without the presence of any other iron(III) oxide admixtures and on the change in its magnetic and electrochemical features, proving their feasible tuning with respect to the requirements of potential future applications.