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

Abstract

The influence of Sc3+ ion content on the microstructure, electrical, and gas-sensing properties of Ni0.5Co0.5ScxFe2–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 Ni0.5Co0.5Fe2O4 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 (Ni0.5Co0.5Fe2O4) results in the increase of the response and the decrease of the optimal operating temperature for all the studied gases. The sensor element Ni0.5Co0.5Sc0.2Fe1.8O4 (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%.