Single Crystal Diffraction Studies of WO3at High Pressures and the Structure of a High-Pressure WO3Phase

Xu, Yongnan; Carlson, Stefan; Norrestam, R.

doi:10.1006/jssc.1997.7420

Cited by 47 publications

(71 citation statements)

References 12 publications

(9 reference statements)

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“…37 A transition to a compressed phase can be obtained either by using high external pressure or by accumulating internal compressive strain due to polarons. 23,47 It has been reported that slightly reduced WO 3Àx , with x % 0.05, promotes formation of the e phase, 29 qualitatively consistent with our data. There is no change of the octahedral tilt angle between the d-WO 3 and e-WO 3 phases.…”

Section: Resultssupporting

confidence: 91%

“…WO 3 exists in several phases, which differ with respect to each other by the tilting and displacement of the atoms in the octahedral building blocks that comprise the WO 3 structure. The thermodynamically favored phase is reported to change with temperature (at standard pressure) for crystalline bulk WO 3 as follows: monoclinic Pc (e-WO 3 ) up to 230 K, triclinic P1 (d-WO 3 ) 230-300 K, monoclinic P2 1 /n (c-WO 3 ) 300-623 K, orthorhombic Pnma (b-WO 3 ) 623-1020 K, tetragonal P4/ncc (a-WO 3 ) 1020-1171 K, and, finally, tetragonal P4/nmm (a-WO 3 ) to the melting point at 1700 K. [22][23][24][25][26] The stability of each of these phases is modified by preparation procedures. For nanocrystalline thin films, the detailed growth conditions are critical, including type of substrate, temperature, and pressure.…”

Section: Introductionmentioning

confidence: 99%

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Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

2012

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Nanostructured tungsten trioxide films were prepared by reactive dc magnetron sputtering at different working pressures P tot 5 1-4 Pa. The films were characterized by scanning electron microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, Raman spectroscopy, and ultraviolet-visible spectrophotometry. The films were found to exhibit predominantly monoclinic structures and have similar band gap, E g % 2.8 eV, with a pronounced Urbach tail extending down to 2.5 eV. At low P tot , strained film structures formed, which were slightly reduced and showed polaron absorption in the near-infrared region. The photodegradation rate of stearic acid was found to correlate with the stoichiometry and polaron absorption. This is explained by a recombination mechanism, whereby photoexcited electron-hole pairs recombine with polaron states in the band gap. The quantum yield decreased by 50% for photon energies close to E g due to photoexcitations to band gap states lying below the O 2 affinity level.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

2012

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“…At 0.1 GPa the transformation into HP1 phase is complete. The same phase transition was observed by Salje [7], Souza Filho [g] and Xu [2], but at higher-pressure values: 0.155 GPa and 1.01 GPa respectively. According to the above literature the HP1 phase is observed up to 5 GPa.…”

Section: Discussionsupporting

confidence: 82%

“…> tetragonal (P4/nmm, Z=2) [2,. The existent data on high-pressure (HP) measurements of tungsten trioxide phase transition are not so clear.…”

Section: °'Okmentioning

confidence: 99%

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

et al. 2001

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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

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Coexistence of triclinic and monoclinic phases in WO3 ceramics

Filho

Freire

Sasaki

et al. 2000

J. Raman Spectrosc.

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Single Crystal Diffraction Studies of WO3at High Pressures and the Structure of a High-Pressure WO3Phase

Cited by 47 publications

References 12 publications

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

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

Coexistence of triclinic and monoclinic phases in WO3 ceramics

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Single Crystal Diffraction Studies of WO3at High Pressures and the Structure of a High-Pressure WO3Phase

Cited by 47 publications

References 12 publications

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

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

Coexistence of triclinic and monoclinic phases in WO3 ceramics

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Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering