Humidity and Temperature Sensing of Mixed Nickel–Magnesium Spinel Ferrites

Temperature- and humidity-sensing properties were evaluated of NixMg1-x spinel ferrites (0 ≤ x 1) synthesized by a sol-gel combustion method using citric acid as fuel nitrate ions oxidizing agents. After the exothermic reaction, amorphous powders calcined at 700 °C followed characterization with XRD, FTIR, XPS, EDS Raman spectroscopy FESEM microscopy. Synthesized tested humidity- temperature-sensing materials in form thick films on interdigitated electrodes alumina substrate climatic chamber. The physicochemical investigation revealed cubic Fd3¯m phase, nanosized but agglomerated particles partially to completely inverse structure increasing Ni content. Ni0.1Mg0.9Fe2O4 showed highest material constant (B30,90) value 3747 K temperature sensitivity (α) −4.08%/K compared pure magnesium ferrite (B30,90 3426 α −3.73%/K) average towards humidity 922 kΩ/%RH relative (RH) range 40–90% working 25 °C.