Humidity sensor using potassium hexagonal tungsten bronze synthesized from peroxo-polytungstic acid and its resistivity change mechanism

We have found that potassium hexagonal tungsten bronze (K-HTB) synthesized from potassium peroxo-polytungstate at low temperature (500 °C) shows a remarkable increase in resistivity in a humid atmosphere at room temperature. The mechanism of the resistivity increase by incorporation of water was investigated by gravimetry, complex impedance spectroscopy, and powder XRD measurement. The powder XRD profiles indicated that superlattice structure of the K-HTB emerges by incorporation of water. A layer structure model of the K-HTB was suggested from these results.