Humidity-sensing properties of ZnCr2O4-ZnO composites

The preparation of ZnCr2O4 was carried out by the high-temperature solid-state method with the reaction of Cr2O3 and ZnO at 900 degreesC. Experimental results on the composites made from different mole ratios of ZnCr2O4 and ZnO for electrical and humidity-sensing properties are described. The sintered polycrystalline disks of the composites were subjected to DC electrical conductivity measurements over the temperature range 330-500 K from which the activation energies were determined. The composites were identified by powder X-ray diffraction (XRD). The scanning electron microscopy (SEM) studies were carried out to study the surface structure of the sensor materials. The composites were subjected to DC resistance measurements as a function of relative humidity in the range of 5-98% RH, achieved by different water vapor buffers thermostated at room temperature. The sensitivity factor S-Gamma (R-5%/R-98%) measured at 298 K revealed that ZCZO-21 has the highest humidity sensitivity, greater than 6.5 x 10(3); however, ZCZO-11, ZCZO-32, and ZCZO-14 have lower sensitivity but better linear trend. The response and recovery characteristics for ZCZO-21 and ZCZO-11 were assessed. (C) 2003 Elsevier Science B.V. All rights reserved.