Moisture sensor based on ZnO nanomaterial synthesized through oxalate route

The ZnO nanomaterial has been synthesized through pyrolysis of the oxalate produced by a conventional precipitation method. It is synthesized by flash heating the oxalate at 450 °C for 15 min. The pellets from this powder have been calcined at temperatures 150, 300, 450 and 550 °C for 3 h and tested for its sensing ability. Each heat-treated pellet is exposed to humidity under controlled condition and variations in resistance with variations in humidity have been measured. From Arrhenius plot, it is found that the activation energy for electrical transport is maximum (0.00976 eV) when calcinations are performed at the temperatures between 300 and 550 °C, which inferring shallow donor or acceptor levels. Average sensitivity of the sensing element is maximum (7.06 MΩ/%RH) when the sample is calcined at 550 °C. Reversibilities of the resistances with %RH for different annealing temperatures have also been observed. Reversibilities are excellent when the samples are heat-treated above 450 °C. Scanning electron micrographs of the sensing elements have been studied. Pellets of the ZnO nanomaterial are comprised of nanorods of varying diameters and different lengths. Diameter of ZnO nanorods varies from 75 to 300 nm. X-ray diffraction patterns of the sensing elements reveal their nano-crystalline nature.