Humidity sensing behavior of thick films of strontium-doped lead-zirconium-titanate

PSxZ0.3T0.7O3 (x=0.1–0.5) nano-particles were prepared using sol–gel technique from alkaoxides. The powders were calcined at different temperatures from 500 to 700 °C. The optimum calcination temperature of 600 °C was chosen based on the differential thermal analysis and XRD analyses. The structural and morphological analyses of powders were carried out using XRD and scanning electron microscope. The particle size found to be approximately 30–45 nm, varies as an inverse function of Sr doping concentration. Sensors were fabricated in the form of thick film resistors (of ∼25-μm thickness) on the alumina substrate having pre-printed Ag electrodes. The I–V characteristic of these resistors was obtained by varying voltage from −5 to +5 V. The band gap is found to vary from 2.7 to 3.7 eV which decreases with increasing Sr doping level. The samples were tested for sensing relative humidity (RH) in the range of 20–100% RH. The sensitivity, measured as a function of d.c. resistance, increases with increasing Sr concentration. The sensitivity and barrier height are correlated.