Among the family of wide band-gap semiconducting metal oxides, tungsten trioxide is the most promising oxide for gas
sensing. A metastable open-structured hexagonal phase of WO3 was successfully synthesized using acid precipitation
method. The oxide was characterized using SEM, TEM and XRD. The sensing property to reducing ammonia gas was
measured. The sensitivity is much higher than that of monoclinic tungsten oxides. The oxide polymorph exhibits a p-n
type transition when the temperature goes from 100 °C to 300 °C.