Comparative Study on Micromorphology and Humidity Sensitive Properties of Thick and Thin Film PbWO_4-WO_3 and ZnWO_4-WO_3 Composites

摘要

Sintered materials of PbWO_4, ZnWO_4 and WO_3 were mixed in the molar ratios 80:20, 60:40, 40:60, 20:80 and doped with 2 mol% of Li~+. Thick and thin films of the PbWO_4-WO_3 (PWWO) and ZnWO_4-WO_3 (ZWWO) composites were fabricated through sol-gel technique. The prepared composites were characterized by powder XRD, solid state electrical measurement, SEM studies to analyze phase transition, activation energy for conduction, surface morphology of the sensor materials, respectively. The humidity sensing properties were measured employing the sensor configurations of a thick and thin film. The thin film sensor showed a smaller humidity sensitivity factor than that of the thick film. However, the former exhibited a fast response to humidity change and also had a very low temperature coefficient in the temperature range of 20-60℃. The thin and thick films were subjected to dc resistance measurements as a function of relative humidity in the range of 5-98% at 300 K. It was found that the Li~+-doped thick film PWWO-28 (PbWO_4:WO_3 = 20:80) and ZWWO-46 (ZnWO_4:WO_3 = 40:60) had the highest sensitivity factor of 33500 (±3000), and 12800 (±550). Studies on thin film sensors based on PbWO_4-WO_3 and ZnWO_4-WO_3 indicated that the W~(6+) sites in the hubnerite material contributed strongly to the humidity sensing mechanism.