Fabrication of rare earth(R--Ce,Gd, Ho and Sm) doped CoCr2-x RxO4 pigments for capacitive and resistive humidity sensor applications

Rare earth (Ce, Gd, Ho & Sm) doped CoCr2O4 green pigments with an extremely porous nature powder were produced using a quick and affordable chemical synthesis procedure called solution combustion. X-ray diffraction analyses revealed the phase composition and average crystallite size. SEM images of the samples that had been annealed at 600 degrees C revealed the existence of cuboids and soft agglomerations. Using an LCR metre to analyse the dielectric properties of assynthesised samples, it is discovered that the small crystallite size exhibits a higher dielectric constant. The results were impressive when permittivity and electrical resistivity fluctuated with frequency under humid circumstances. By varying the relative humidity from 0 to 100%, electrical measurements were performed to investigate the rare earth pigments' capabilities for sensing humidity. Sample electrical resistance decreases over the entire humidity range. At room temperature, the resistive responses were measured at various relative humidity (RH) levels ranging from 0% to 98% and at various frequencies ranging from 20 Hz to 20 MHz. The rare earth-doped green pigments used in the humidity sensor have a linear response, high sensitivity, and low hysteresis. In addition, the sensor has 35 and 240 s reaction and recovery times, respectively. Our research indicates that this material could be employed as a capacitive and resistive humidity sensor. The results of this work open the door for the use of rare earth doped cobalt chromate pigments in applications for humidity sensing.