WO sub(3) nano-ribbons: their phase transformation from tungstite (WO sub(3).H sub(2)O) to tungsten oxide (WO sub(3))

Tungsten oxide (WO sub(3)) nano-ribbons (NRs) were obtained by annealing tungstite (WO sub(3).H sub(2)O) NRs. The latter was synthesized below room temperature using a simple, environmentally benign, and low cost aging treatment of precursors made by adding hydrochloric acid to diluted sodium tungstate solutions (Na sub(2)WO sub(4).2H sub(2)O). WO sub(3) generates significant interests and is being used in a growing variety of applications. It is therefore important to identify suitable methods of production and better understand its properties. The phase transformation was observed to be initiated between 200 and 300 super( degree )C, and the crystallographic structure of the NRs changed from orthorhombic WO sub(3).H sub(2)O to monoclinic WO sub(3). It was rigorously studied by annealing a series of samples ex situ in ambient air up to 800 super( degree )C and characterizing them afterward. A temperature-dependent Raman spectroscopy study was performed on tungstite NRs between minus 180 and 700 super( degree )C. Also, in situ heating experiments in the transmission electron microscope allowed for the direct observation of the phase transformation. Powder X-ray diffraction, electron diffraction, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy were employed to characterize precisely this transformation.