Characterization of ammonium tungsten bronze [(NH 4) 0.33WO 3] in the thermal decomposition course of ammonium paratungstate

Abstract

Ammonium tungsten bronze, (NH 4) 0.33WO 3, was characterized in the calcination product of ammonium paratungstate at 400°C for 2 h in a static atmosphere of air. X-ray diffractometry, thermogravimetry, and infrared and UV–vis diffuse reflectance spectroscopies found the yellowish orange product to also contain hexagonal tungsten trioxide, WO 3. On heating up to 500°C, the bronze together with the hexagonal WO 3 were transformed completely into the yellowish green monoclinic tungsten trioxide.