High-pressure study of microcrystalline tungsten trioxide phase transitions by Raman spectroscopy

A high-pressure Raman study of microcrystalline tungsten oxide was performed in the 0.1 MPa-31 GPa pressure range under isostatic and non-isostatic conditions. The phase transitions, which take place below 0.1 GPa and at 22 GPa are first order, while two further structural changes, observed at about 3 and 10 GPa, are diffuse. Surprisingly, the non-isostatic conditions do not induce inhomogeneous band broadenings and do not modify the transitions sequence observed in isostatic conditions. Compressibility of the different phases is estimated from spectral data

High-temperature anodized WO3 nanoplatelet films for photosensitive devices

Anodization at elevated temperatures in nitric acid has been used for the production of highly porous and thick tungsten trioxide nanostructured films for photosensitive device applications. The anodization process resulted in platelet crystals with thicknesses of 20−60 nm and lengths of 100−1000 nm. Maximum thicknesses of 2.4 μm were obtained after 4 h of anodization at 20 V. X-ray diffraction analysis revealed that the as-prepared anodized samples contain predominantly hydrated tungstite phases depending on voltage, while films annealed at 400 °C for 4 h are predominantly orthorhombic WO3 phase. Photocurrent measurements revealed that the current density of the 2.4 μm nanostructured anodized film was 6 times larger than the nonanodized films. Dye-sensitized solar cells developed using these films produced 0.33 V and 0.65 mA/cm2 in open- and short-circuit conditions