Elucidation of room temperature humidity sensing properties of Mn₂O₃ particles

MnCO₃ particles were thermally decomposed to obtain Mn₂O₃ particles. MnCO₃ was prepared by co-precipitation method using MnCl₂.4H₂O and CO(NH₂)₂ as reactants. Two separate parts of the obtained MnCO₃ were calcined at 450 °C and 550 °C. The structural, crystallographic, morphological properties and elemental composition of all the materials were investigated using Fourier transform infrared spectrometry (FTIR), X-ray diffraction analysis (XRD), scanning electron microscopy and energy-dispersive X-rays spectroscopy (EDX). FTIR spectrum of the precursor and calcined products was related to MnCO₃ and Mn₂O₃, respectively. As per XRD study, the precursor and calcined product obtained at 550 °C was crystalline, while the product obtained at 450 °C was amorphous in nature. From topographic study, the particles of MnCO₃ and Mn₂O₃ were of cuboid shape. Elemental analysis of the samples via EDX analysis confirmed that the weight and atomic percentages of the precursor and calcined products are related to MnCO₃ and Mn₂O₃, respectively. Afterward, the calcined products were used for investigation of their humidity sensing behavior at room temperature. The product obtained at 550 °C demonstrated reproducible, highly sensitivity and stable response toward humidity having response and recovery time 3 s and 13 s, respectively. Percent sensitivity of this material increased up to 96% by varying the humidity from 35 to 96%. The sensing mechanism was suggested to be based on protonic model, wherein the generation of H⁺ ions due to the dissociation of H₃O⁺ ions reduces the sensor resistance and enhances the humidity sensitivity.