Cerium doped cobalt chromate for resistive and capacitive humidity sensor applications

The effect of cerium (Ce³⁺) on the structural, microstructural, Fourier infrared spectroscopic, electrical, and humidity sensing behavior of CoCr_2−xCe_xO₄(CoCrCe) is reported in this paper. To prepare the samples, Solution combustion method using mixture of urea and glucose as a fuel. Samples are sintered for 600 °C for 3 h to get single phase. To analyses the creatinine nature and morphology, samples were characterize X-ray diffraction (XRD) and scanning electron microscopy. XRD reveals that formation of cubic spinel structures with typical crystallite sizes of less than 10 nm. When Ce³⁺ ions are replaced by Cr³⁺ ions, the lattice parameter found decreases from 8.3289 to 8.3163 Å. This is due to the creation of a compressive lattice strain and may be due to the differences between ionic radius of Ce³⁺ as compared to Cr³⁺. We discovered the chrommate structure in the absence of impurities by analysing the octahedral and tetrahedral stretching bands using Fourier infrared spectroscopy. Scanning Electron microscopy results reveals that samples exhibits highly porous nature. Elemental analysis were confirms the Ce³⁺ is present in the samples. All samples subjected to study the humidity sensing studies. The relative humidity influences the resistivity of the surrounding air significantly. We also investigated the relative permittivity characteristics, the conductivity of the samples of interest, and the capacitive sensor’s response time at a fixed frequency of f = 1 kHz. Further, The variation of both relative permittivity and electrical resistivity were strongly depending on humidity. As concentration of Ce³⁺ increases the permittivity (unit less), Conductivity, electrical capacity(normalized), Response time of capacitive sensor were found increases such as 150, 10⁸ [Ω m], 10, 90 this is may be due to the larger ionic radius of the Ce³⁺ and also may be high porosity of the samples. Ce³⁺ at 2 mol% has improved humidity sensing properties as compared to other concentration. We conclude that CoCr_1.98Ce_0.02O₄ be useful for an active material in humidity-sensing devices.