Solid state electrical conductivity and humidity sensing properties of WO3-Y2O3 composites

Experimental results on the composites made from WO3 (WO) and Y2O3 (YO) for electrical and humidity sensing properties are described. The compound and composites of WO3 and Y2O3 in mole ratios (1: 1, 1:2, 2:1, 1:3, 3:1 and 3:2%) were sintered in the form of a disc of 10 mm diameter were subjected to do conductance measurements over the temperature range 373-673 K from which the activation energies were determined. The composites were identified by powder XRD data. The scanning electron microscopy (SEM) studies were carried out to study the surface and pores structure of the sensor materials. The Brunauer-Emmett-Teller (BET) surface adsorption studies showed that the radius of the pore sizes were found to be distributed from 10-45 Angstrom. The pore specific volume was calculated to be 0.01 cm(3) gm(-1). As the composites having micropores are preferred for humidity sensing properties, the composites were subjected to do resistance measurements as a function of relative humidity in the range of 5-98% RH, achieved by different water vapour buffers thermostated at room temperature. The sensitivity factor S-f (R-5%/R-98%) measured at 25 degreesC revealed that WOYO-31 (WO3 and Y2O3 in 3:1 mole ratio) has the highest humidity sensitivity factor of 1535 (+/-80). The response and recovery time for this humidity sensing composite was also studied. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.