Highly sensitive humidity sensor based on lithium stabilized Na-β″-alumina: dc and ac analysis

The humidity property of the lithium stabilized Na-β″-alumina (LSBA) sensing material was investigated in detail on a resistivity-type sensor prepared by pasting LSBA powder on a ceramic substrate with Ag interdigitated electrodes through ac and dc analysis. Results from ac complex impedance analysis suggested that LSBA powder based sensor was highly sensitive to humidity with a six order magnitude impedance difference as relative humidity (RH) changed from 11.3% to 93.6% and good stability in 30 days. The response time and recovery time of the sensor were short at lower RH circumstance, which were 42 s and 48 s at 52.8% RH, respectively. Evidences from dc variation, ac dielectric loss and ac complex impedance spectra under different RH circumstance indicated that high humidity sensitivity of the LSBA sensor originated not only from the water molecules absorbed on the surface but also from the Na⁺ ions in the conduction slab of the LSBA crystal.