Microstructural and electrical properties of sintered tungsten trioxide

Abstract

Tungsten trioxide sintered wafers were prepared from WO3 powder obtained when ammonium paratungstate is decomposed in air at moderate temperature. Two wafer series of five samples were sintered under the same conditions in the temperature range 600–1000 C. One of these wafers series was submitted to a subsequent annealing at 700 C under a hydrogen atmosphere. All samples were characterized at room temperature by X-ray diffraction and electrical measurements. X-ray spectra show that WO3 ceramic presents a mixture of the triclinic and monoclinic phases before the reduction process. After the reduction process, WO2 and four hydrogen tungsten bronze phases are present in wafers. Capacitance measurements showed that the samples submitted only to the sintering process changed the dielectric constant with the frequency according to the Debye model. The reduced WO3 shows a semiconductor behavior, as determined by electrical resistivity measurements.