The influence of Sc3+ ions on the microstructure, electrical, and gas-sensing properties of Ni–Co–Sc ferrite.

The influence of Sc³⁺ ion content on the microstructure, electrical, and gas-sensing properties of Ni_0.5Co_0.5Sc_xFe_2–xO₄ (x = 0.0, 0.05, 0.1 and 0.2) ferrites synthesized by a novel self-combustion method using polyvinyl alcohol as the colloidal medium, was studied. X-ray diffraction, X-ray photon spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) were employed to characterize the structure and morphology properties of these ferrites. The gas-sensing properties of hydrogen, methane, ethanol, methylene chloride, and benzene were investigated. The samples show p-type semiconducting properties for the studied gases within the temperature range of 100–380 °C. The results revealed that the partial substitution of Fe³⁺ by Sc³⁺ ions on the octahedral sites of the spinel structure of Ni_0.5Co_0.5Fe₂O₄ ferrite has a favorable effect on the sensing activity of this ferrite. The increase of the degree of Fe³⁺ ion substitution by Sc³⁺ ions up to x = 0.2 in the basic composition (Ni_0.5Co_0.5Fe₂O₄) results in the increase of the response and the decrease of the optimal operating temperature for all the studied gases. The sensor element Ni_0.5Co_0.5Sc_0.2Fe_1.8O₄ (x = 0.2) has the best response to benzene (2.57) and to methylene chloride (2.10) at the operating temperature of 175 °C for a gas concentration of 500 ppm and a relative humidity of 50%. Highlights: The Ni_0.5Co_0.5Sc_xFe_2–xO₄ (0 < x < 0.2) ferrites have been prepared by self-combustion method. The porosity is amplified by a system with open pores distributed along the grain agglomerations. The increase of substitution by Sc results in the increase of sensor response to the studied gases. The substitution with Sc ions has the effect of decreasing the optimal operating temperature. The Ni_0.5Co_0.5Sc_0.2Fe_1.8O₄ sensors have the best response to benzene and methylene chloride gas. [ABSTRACT FROM AUTHOR]