Phase transformation of TiO 2 powder (P25) and pure anatase (PA) was investigated under pure oxygen as well as vacuum from 500 to 1,000°C. The rutile percentage calculated based on the XRD data was used to estimate the phase transformation process. It was found that the vacuum suppressed the phase transformation of P25 relative to pure oxygen atmosphere. A model was proposed to explain the effect of oxygen on the phase transformation of TiO 2 . Furthermore, P25 samples showed lower phase transformation temperature (between 600 and 800°C) compared with PA (over 1,000°C). The existed rutile phase in P25 was regarded as a transformation inducer due to an interface between anatase and rutile phases since the nucleation activation energy on the interface is lower than that on the surface. And this interface effect is also adopted to explain the role of additive WO 3 , which retarded the phase transformation of P25 but promoted the phase transformation of PA.

Nano-structured tungsten oxide (WO 3 ) thin films were deposited at room temperature by glancing angle reactive magnetron sputtering and then annealed at 450℃ in air. The films were characterized by field-emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The WO 3 thin film deposited by DC magnetron sputtering at 80° glancing angle exhibited oblique nano-column structure, while deposited by pulsed DC magnetron sputtering at the same angle exhibits nano-pore structure. After annealing at 450℃ for 3 h, the oblique nanocolums are conjunct with each other but the nano-pore structured remains with bigger pore size. XRD analysis reveals that WO 3 thin films deposited at room temperature demonstrate amorphous structure. The amorphous structure will transfers to monoclinic phase after annealing at 450℃ for 1 h. Transmittance difference between colorization and bleaching of nano-structured WO 3 thin film reaches 60% at wavelength of 600 nm. Electrochromic properties of nano-structured WO 3 thin films are highly reversible.

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