Raman studies were performed on titania thin films prepared by polyethylene glycol (PEG) assisted, low-temperature, sol-gel method. The Raman spectra of the films show a systematic blue shift in the peak position and a broadening in the full width at half-maximum (FWHM) when compared with those of the bulk anatase TiO 2 powder. Several reports have appeared indicating this kind of peak shift and broadening of FWHM, which were attributed to the confinement of phonons in the anatase nanocrystallites. In this paper, we report an analysis of quantum size effect in the Raman spectra of nanocrystalline TiO 2 thin films performed by utilizing the phonon dispersion relation of the anatase phase which has been obtained from a work based on density functional perturbation theory (DFPT). For comparison purposes the quantum size effect calculations have also been done utilizing the dispersion relations of the rutile phase. There is good agreement between the crystallite sizes evaluated from the equally weighted Raman line intensity of the dispersion relations obtained from the DFPT and those determined by X-ray diffraction.

Macroporous hexagonal WO 3 (h-WO 3 ) films were obtained at 400 °C from a sol containing tungstic acid with organically modified silane as a template. Asymmetric electrochromic devices based on the macroporous h-WO 3 layer were constructed. XRD and micro-Raman studies of the intercalation/ deintercalation of lithium into the h-WO 3 layer of the device as a function of the applied voltages were performed. In h-WO 3 , Li + can be intercalated into three potential sites: trigonal cavity (TC), hexagonal window (HW), and four-coordinated square window (SW). XRD measurements show systematic changes in the lattice parameter, which was associated with the amount of Li intercalated into the h-WO 3 layer. Correspondingly, Raman spectroscopy shows that at 1.0 V Li + completely fill TC and partially fill HW sites. For potentials g1.5 V, Li + are inserted into the SW, as evidenced from the vanishing of the ν(O-W-O) Raman modes. The reversible characteristics of the device from optical measurements and Raman spectra demonstrated that the coloration process in the electrochromic device is mainly due to the Li + that occupy HW and SW sites of the h-WO 3 . Optical measurements performed as a function of applied potentials, show excellent contrasts between colored and bleached states and qualifies the macroporous h-WO 3 -based device for smart window applications.

Porous orthorhombic tungsten oxide (o-WO 3 ) thin films, stabilized by nanocrystalline anatase TiO 2 , are obtained by a sol-gel based two stage dip coating method and subsequent annealing at 600 C. An Organically Modified Silicate (ORMOSIL) based templating strategy is adopted to achieve porosity. An asymmetric electrochromic device is constructed based on this porous o-WO 3 layer. The intercalation/deintercalation of lithium ions into/from the o-WO 3 layer of the device as a function of applied coloration/bleaching voltages have been studied. XRD measurements show systematic changes in the lattice parameters associated with structural phase transitions from o-WO 3 to tetragonal Li x WO 3 (t-Li x WO 3 ) and a tendency to form cubic Li x WO 3 (c-Li x WO 3 ). These phase transitions, induced by the Li ions, are reversible, and the specific phase obtained depends on the quantity of intercalated/ deintercalated Li. Raman spectroscopy data show the formation of t-Li x WO 3 for an applied potential of 1.0 V and the tendency of the system to transform to c-Li x WO 3 for higher coloration potentials. Optical measurements show excellent contrasts between colored and bleached states. An alternate photochromic device was constructed by sensitizing the o-WO 3 layer with a ruthenium based dye. The nanocrystalline anatase TiO 2 in the o-WO 3 layer has led to an enhanced photochromic optical transmittance contrast of $51% in the near IR region. The combination of the photochromic and electrochromic properties of the synthesised o-WO 3 layer stabilized by nanocrystalline anatase TiO 2 opens up new vista for its application in energysaving smart windows.

Recent developments in the synthesis of transition metal oxides in the form of porous thin films have opened up opportunities in the construction of electrochromic devices with enhanced properties. In this paper, synthesis, characterization and electrochromic applications of porous WO3thin films with different nanocrystalline phases, such as hexagonal, monoclinic, and orthorhombic, are presented. Asymmetric electrochromic devices have been constructed based on these porous WO3thin films. XRD measurements of the intercalation/deintercalation of Li+into/from the WO3layer of the device as a function of applied coloration/bleaching voltages show systematic changes in the lattice parameters associated with structural phase transitions in LixWO3. Micro-Raman studies show systematic crystalline phase changes in the spectra of WO3layers during Li+ion intercalation and deintercalation, which agree with the XRD data. These devices exhibit interesting optical modulation (up to ~70%) due to intercalation/deintercalation of Li ions into/from the WO3layer of the devices as a function of applied coloration/bleaching voltages. The obtained optical modulation of the electrochromic devices indicates that, they are suitable for applications in electrochromic smart windows.