Evaluation of structural, dielectric and electrical humidity sensor behaviour of MgFe2O4 ferrite nanoparticles

Green synthesis procedure assisted with lemon juice was adopted to prepare MgFe2O4 ferrite nanoparticles. Structural analysis revealed the purity of the ferrite phase of the samples without any secondary phases. Lemon juice as a chelating agent seems to be playing crucial role in the formation ferrite phase. The crystallinity of ferrite samples was found to be ripened with the heat treatment and higher average size of 32.9 nm was reported for crystallite size. The average particle size (estimated from the SEM histograms) is well matched with the average crystallite size (estimated from the XRD peaks). The dielectric behaviour is similar to the usual spinel ferrite systems, as the dielectric constant is maximum at lower frequencies and decreases at higher frequencies due to hopping of electrons showing the dielectric dispersion. This dielectric behaviour is influencing the humidity sensing behaviour in the way of interfacial polarization of water molecules for conduction mechanism to increase the impedance of the material with the decrease of dielectric constant. Moreover, in the present ferrite systems hopping mechanism appears to be dependent on the location of Mg2+ ion in the spinel structure. The asprepared and sintered samples are showing a humidity response over the humid range of 10?95% RH. The sample sintered at 900 ?C is showing highest average sensor response 6.02 M?/%RH among the as-prepared sample (5.56 M?/%RH) and sintered sample at 600 ?C (5.70 M?/%RH).