Synthesis, Characterization and Effect of Sintering Temperature on the Humidity Sensing Properties of Nanocrystalline PbO

An alcohol thermal route has been used to synthesize nanocrystalline PBO at a relatively low temperature of 75 degrees C using lead acetate. The synthesized lead oxide (P75) was subjected to different heat treatments ranging from 200-500 degrees C for 2 h to study the effect of crystallinity and phase changes and were further labeled as P200, P300, P400 and P500, respectively. X-Ray diffraction, FT-IR spectroscopy, scanning electron microscopy and transmission electron microscopy were carried out to identify the structural phases, vibrational stretching frequencies, surface morphology and particle size, respectively. The TEM images revealed the change in morphology of PbO from rhombus to rod shape at higher temperatures. The SEM images revealed the porous nature of P75 sample, which is an important criterion for the humidity sensor. All the samples were subjected to de resistance measurements as a function of relative humidity in the range 5-98 % and the dc resistances at 5 and 98 % relative humidity was used to calculate the sensitivity factor (S-r = R-5%/R-98%). Among the different composites prepared, P75 possessed the highest humidity sensitivity of 4545, while the heat treated sample P500 possessed a low sensitivity of 220. The response and recovery time of the maximum sensitivity sample P75 was studied and was found to be 95 and 78 s, respectively.