In situ construction and sensing mechanism of TiO2–WO3 composite coatings based on the semiconductor heterojunctions

Tungsten oxide (WO 3 ) is one of the most promising gas-sensitivity materials owing to its high decomposition temperature and stability of microstructure. The doping of oxides can significantly improve its gas-sensitivity properties. In this paper, WO 3 based coatings doped with TiO 2 were prepared via plasma spraying technology by using mixed feedstock suspensions containing a precursor as WCl 6 and a certain ratio of nano-TiO 2 . The characterization of microstructures and properties of the TiO 2 –WO 3 composite coatings were achieved and the gas sensitivity mechanism was researched. During the suspension plasma spraying, the solvent of the precursor droplets was evaporated and then the nucleation, crystallization and growth of WO 3 occurred. The crystallinity and crystal grains of WO 3 increased observably as the plasma spraying power improved. With the increase of TiO 2 in coatings, the average grain size of the TiO 2 –WO 3 composite coatings decreased at first and then increased. And the gas-sensitive properties of the composite coatings were significantly better than the pure WO 3 coatings. The gas-sensitive properties improvement of TiO 2 –WO 3 composite coatings doped with TiO 2 was firstly caused by the decrease of grains size, which leaded to an increase of the gas adsorption sites. And the Fermi level effect of the composite metal oxide heterojunction formed by TiO 2 and WO 3 also markedly enhanced the gas sensitivity properties of the composite coatings.