Highly responsive and stable Y3+ doped NiMg–ferrite thick films as an efficient humidity sensor

Abstract

The humidity sensing properties of Ni_1−xMg_xY_yFe_2−yO₄ (x = 0, 0.1 and 0.3 when y = 0; and y = 0.1 and 0.3 when x = 0.3) thick films are investigated. The structural and morphological properties of the resulting materials were determined by XRD, TEM, SEM and BET techniques. These revealed materials of polycrystalline nature with a single phase spinel structure possessing porosity having cubic and spherical shape morphology. XPS analysis suggested that the presence of Y³⁺ on the surface enhances the humidity sensing properties. Thick films exhibit better sensing properties as compared to pellets at lower relative humidity with less hysteresis characteristics at a lower film thickness. Faster response and recovery time are observed for thick films due to the formation of a uniform layer of active sites on the film surface. The long-term stability is evaluated over a period of six months when it is noticed that the response remains almost constant at different ranges of humidity. This feature may be regarded as a significant facet towards their practical application as humidity sensors.