Gas sensitivity of stoichiometric and excess-iron Ni-Zn ferrite prepared by sol-gel auto-combustion

Abstract

Application of new materials offers more sensitive, selective and long-term stable sensor materials. The aim of the present work is to compare gas response to acetone of nanostructured sol-gel auto-combustion derived stoichiometric and excess-iron cubic spinel type nickel-zinc ferrite (Ni0.3Zn0.7Fe2+zO4 where z  =  0 and 0.1). Detailed synthesis steps and gas sensing measurement methodology were described. The sensor material was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and direct current (DC) resistance measurements. XRD analysis confirms that samples form the single-phased cubic spinel structure, SEM reveals nanosized grains less than 100 nm in diameter. Plots of resistance versus temperature show adsorbed water contribution to the conductance. With excess-iron, Ni-Zn ferrite changes its DC electrical resistivity, type of conductivity, as well as response to reducing gas (more than 2 times). Obtained relationships can be explained with Fe2+ formation in the material, thus increasing charge carrier (electron) concentration. This leads down to higher oxygen adsorption ability which can act with test gas.