Effects of Crystallization Atmospheres on the Near-Infrared Absorbtion and Electroconductive Properties of Tungsten Bronze Type MxWO3 (M = Na, K)

The fine particles of tetragonal KxWO3 and cubic NaxWO3 were successfully synthesized by reducing WO42- with BH4- in aqueous solutions, followed by the crystallization of amorphous precursors by calcination under N2, NH3 and H2 (5 vol%)/N2 atmospheres at 600 degrees C for 1 h, respectively. The products showed excellent electrical conductivity, visible light transparency, and near-infrared light shielding characteristics, where the samples crystallized in H2 (5 vol%)/N2 mixed gas showed the highest electric conductivity being superior to commercial conductive oxide ITO. Meanwhile, the samples showed strong absorption of near-infrared light and instantaneous conversion of photo-energy to local heat. The effects of crystallization atmosphere on the near-infrared absorbtion and electroconductivity properties of KxWO3 and NaxWO3 are discussed in detail.