Fine-grained MgCu ferrite with ionic substitutions used as humidity sensor

Oxide compounds, Mg0.5Cu0.5Fe2−xMxO4, in which M=La, Ga, Y and x=0 and 0.2, were prepared by self-combustion method and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electric measurements. The XRD analysis evidenced that the compounds containing Y3+ and La3+ ions are pluriphasic, whereas the others are monophasic. An increase in average grain size and a decrease in the porosity in the Y- and La-substituted compounds were observed from SEM images. The electrical resistivity decreased by La and Y incorporation and increased by Ga incorporation. Concerning the humidity sensitivity of the electrical resistivity, the porous Ga-containing ferrite is the most sensitive to humidity change. For this ferrite the resistivity response time to humidity change is shorter.