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

Abstract

A high-pressure Rarnan study of microcrystalline tungsten oxide was performed in the 0.1 MPa-3 1 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 momfy the transitions sequence observed in isostatic conditions. Compressibility of the different phases is estimated from spectral data. l. INTRODUCTION.WOs is known to be complex in terms of structure and phase transitions. At room temperature the coexistence of monoclinic y (P2Jn, Z=8) and triclinic 6 (P?, Z=8) [l-31 phases was reported. Temperature changes of WO3 structure under atmospheric pressure can be presented as follows: triclinic (Z=8)The existent data on high-pressure (HP) measurements of tungsten trioxide phase transition are not so clear. Xu and al. [2] have found that the triclinic form of W03 transits towards a HP phase at 0.57 GPa. Salje and Hoppmann [7] revealed that initial monoclinic y-phase of WO3 crystal partially transforms firstly to triclinic &phase at 0.1 GPa, and after to Pc phase at 0.155 GPa. Souza-Filho et al. [S] have analyzed the Raman spectra of rnicrocrystallized WO3 in the 0.01-SGPa pressure range. They observed the successive disappearance of monoclinic y-and triclinic 6-phases at 1.4 GPa and development of HP phase until to 1.01 GPa without real arguments to decide about its structure.The aim of this investigation was to follow the effect of hydrostatic and non-hydrostatic compressive stresses on the structure of tungsten oxide more precisely inside a wide pressure interval. EXPERIMENTAL PROCEDUREPowder of tungsten oxide (99.995% pure) was obtained from Aldrich. X-ray diffraction diagram reveals that it is the mixture of monoclinic (y) WO3 phase and of triclinic (6) WO3 phase in the approximate ratio 90.10.Raman spectra were obtained using an XY Dilor multi-channel spectrometer equipped with a CCD detector. The 5 14.53 nm line from an Argon ion laser was used as the excitation source. Incident powers of about 5 mW on the sample were used. A diamond anvil cell @AC) was used for HP experiments. For obtaining isostatic pressure a 4:l ethanol-methanol mixture was used as pressure transmitting medium. Non-isostatic pressure investigations consisted in studying the powder without transmitting medium.Article published online by EDP Sciences and available at http://dx

Electrical and optical properties of mixed phase tungsten trioxide films grown by laser pyrolysis

“…2.1 Vibrational and structural analysis Raman and XRD analysis of tungsten trioxide have been reported numerous times [22][23][24][25][26], and despite the simple stoichiometry, the structure is very complex [27][28][29]. Raman spectroscopy was done on two areas of the sample as denoted by spot 1 and spot 2 of the Raman image shown in the inset of Figure 2.…”

High-pressure Raman study of microcrystalline WO3 tungsten oxide

“…Tungsten trioxide, WO 3 , is the focus of an intensive research effort because of its great applicability in electrochromic devices, catalysis, and as a precursor for hard-material synthesis, etc. Recently, nanocrystalline oxides such as tin oxide, zirconia, and tungsten oxide were used in gas sensors; this has stimulated studies of the effect of the nanometric size of crystallites on the P -T phase diagram and on the chemical reactivity of such oxides [1][2][3][4].…”

Experimental and theoretical investigation of a mesoporous KxWO3material having superior mechanical strength

“…2a, in a similar fashion to that reported previously. 27 The same pressure ranges are also indicated in Fig. 2b, which shows the X-ray scattering data beyond the SAXS measured as a function of pressure from the sample.…”

“…Similar evolution of the pressure-dependent Raman data has been reported for microand nano-crystalline WO 3 , whose origin is yet to be determined. 27,31,32 One marked difference is the HP-A to HP-B transition discovered for the mesoporous K 0.07 WO 3 : This has not been reported from the Raman results for micro-or nano-crystalline WO 3 . 27,31,32 The HP-B to HP-C transition is consistent with the HP-1 to HP-2 transition reported from the pressure-dependent Raman measurements of WO 3 nanowires.…”

“…27,31,32 One marked difference is the HP-A to HP-B transition discovered for the mesoporous K 0.07 WO 3 : This has not been reported from the Raman results for micro-or nano-crystalline WO 3 . 27,31,32 The HP-B to HP-C transition is consistent with the HP-1 to HP-2 transition reported from the pressure-dependent Raman measurements of WO 3 nanowires. 32 The contribution from the surface energy of nanomaterials in influencing phase transitions at high pressures (i.e., promotion to higher transition values) has been noted previously.…”