LACUNAR PYROCHLORE-TYPE TUNGSTEN-OXIDES AS HUMIDITY-SENSING MATERIALS

The humidity-sensing characteristics of lacunar pyrochlore-type tungst en oxides containing small cations were investigated. Pyrochlore-type tungsten oxides having the general formula (M(2)O)(x)WO(3)zH(2)O, wher e M = H+, Li+, Na+, Ag+ and NH4+, were prepared by hydrothermal reacti on followed by ion exchange. The sensing elements were fabricated by s creen printing the oxides on top of a pair of comb-shape electrodes or between 2 electrode layers. It was found that the hydrogen form of th e pyrochlore-type tungsten oxide (H-pyroWO(3)) has the lowest resistiv ity, whereas the lithium form (Li-pyroWO(3)) produced the best lineari ty between the relative humidity and the logarithm of its resistance. The sensors showed good durability and reproducibility for detecting c hanges in relative humidity in the range 5-95%. The response time of t he sensor for 90% of the total impedance change (T-90) is about 2 min for both adsorption and desorption processes.