WO3 nano-spheres into W18O49 one-dimensional nano-structures through thermal annealing.

We elaborate the size controlled synthesis of nano-spheres and nano-crystals of WO3 by ultrasonic spray pyrolysis. The as-deposited particles are predominantly spherical in shape and tend to exhibit less agglomeration and a decrease in diameter as the process temperature is increased. Characterization was carried out using transmission (TEM) and scanning (SEM) electron microscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). One-dimensional nano-structures with the highest yield of WOx nano-wires were observed in a sample synthesized at 500 degrees C but only after thermal annealing of this sample at 500 degrees C for 17 hour in flowing argon. XRD revealed a high deficiency in oxygen in all samples suggesting that the nano-structures are transformed to sub-oxides of tungsten. Micro-diffraction patterns of a typical nano-wire reveal the monoclinic phase of W18O49.