Coexistence of triclinic and monoclinic phases in WO3 ceramics

Filho, A. G. Souza; Freire, V. N.; Sasaki, J. M.; Fílho, J. Mendes; Julião, J. F.; Gomes, Uílame Umbelino

doi:10.1002/1097-4555(200006)31:6<451::aid-jrs528>3.0.co;2-k

Cited by 61 publications

(44 citation statements)

References 13 publications

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“…[33][34][35][36] In addition, two peaks located at 276 cm −1 and 332 cm −1 can be assigned to the O-W-O bending (δ) vibration, which are also signature peaks reflecting a monoclinic structure of this pure WO 3 film. 33,[37][38][39][40] These observations are consistent with the XRD result.…”

Section: Resultssupporting

confidence: 90%

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Gui

Blackwood

2015

J. Electrochem. Soc.

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The electrochromic properties of 90:10 WO 3 /TiO 2 thin films produced by anodizing co-sputtered W/Ti films in a fluorinated ethylene glycol solution are investigated in relation to corresponding pure WO 3 films. SEM images revealed that the TiO 2 content resulted in a more open honey-comb structure that increased the charge accommodation ability by 250%. The superior charge storage property of the WO 3 /TiO 2 meant that it had a better light modulation range, with transmittance of <1% at 800 nm in the colored state. The electrochromic kinetic processes associated with coloration and bleaching are also much faster in the presence of TiO 2 , with data generated by electrochemical impedance spectroscopy revealing that this is due to a reduction in the resistance to the insertion of Li + ions. Materials characterization techniques revealed that the WO 3 /TiO 2 composite maintains the monoclinic structure of the WO 3 and that the Ti atoms are substituted into the WO 3 matrix, rather than forming discrete 8 This especially important in the tropics where air-conditioning usage is high, in part due to architects making extensive use of aesthetically pleasing glass.However, unless the WO 3 is made via expensive high vacuum techniques, some of its properties, such electrochromic reversibility, stability or optical modulation, fall short of those required for a practical smart window. Since these drawbacks have proven difficult to overcome in a pure WO 3 system there have been a number of attempts to solve them by doping or mixing with other electrochromic materials, usually another transition metal oxide. [9][10][11][12][13][14][15][16] In 2005, Patil et al.17 investigated the effect of TiO 2 additions on the electrochromic properties of tungsten trioxide films prepared through spray pyrolysis, finding improved electrochromic reversibility, but not any real enhancement of the coloration efficiency. 17One possible way to improve electrochromic efficiency is to tailor the morphology of the oxide to have spacious channels that can aid charge/ion injection into and transport within the film.18-20 One approach to achieve this is by electrochemical anodization. In 2009 Zheng et al., 7 successfully formed a macro-porous WO 3 thin film by anodizing pure tungsten, which had been deposited onto conductive fluorine doped tin oxide (FTO) glass by a magnetron sputtering method, in NH 4 F aqueous electrolyte. This success provides and broadens the application of electrochromic WO 3 thin films on "Smart Windows" where the transparent substrate is essential. However, these authors only focused on the fabrication of WO 3 thin film with macro-porous structure on FTO glass, giving neither details nor further exploration of the electrochromic properties.Besides efforts have been directed at improving electrochromic properties by producing mixed transition metal oxide films, most notably WO 3 /TiO 2 , by techniques such as electron beam deposition, sputtering, hydrothermal and the sol-gel method. 17,[21][22][23] Although the synthesized film...

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Section: Resultssupporting

confidence: 90%

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Gui

Blackwood

2015

J. Electrochem. Soc.

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“…e peak at 440 cm −1 in the spectrum of doped pellet is assigned to tungsten trioxide (W 5+ O), also visible in the Raman spectra of TiW-Nb4 and TiW-Nb6 (Figure 4(b)). e asymmetric shoulder formed is more evident for the higher doped sensor and might be associated with the proximity of the monoclinic WO 3 (mode G) vibrational mode at 605 cm −1 [17,18].…”

Section: Microstructural Characterizationmentioning

confidence: 91%

Preparation, Characterization, and Evaluation of Humidity-Dependent Electrical Properties of Undoped and Niobium Oxide-Doped TiO₂ : WO₃ Mixed Powders

Faia

Libardi

Barbosa³

et al. 2017

Advances in Materials Science and Engineering

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e study of selective metal oxide-based binary/ternary systems has received increasing interest in recent years due to the possibility of producing e cient new ceramic materials for relative humidity (RH) detection, given the superior properties of the mixed compounds in comparison with pristine ones. e aim of this work was focused on preparation and characterization of non-doped and Nb 2 O 5 -doped TiO 2 : WO 3 pair (in the pellet form) and evaluation of corresponding humidity-dependent electrical properties. e microstructure of the samples was analyzed from scanning electron microscopy, X-ray di raction patterns, Raman spectra, BET surface area analysis, and porosimetry. e electrical characterization was obtained from impedance spectroscopy (100 Hz to 40 MHz) in the 10-100% RH range. e results showed that adequate doping levels of Nb 2 O 5 introduce important advantages due to the atomic substitution of Ti by Nb atoms in highly doped structures with di erent levels of porosity and grain sizes. ese aspects introduced a key role in the excursion (one order of magnitude) in the bulk resistance and grain boundary resistance, which characterizes these composite ceramics as a promising platform for RH identi cation.

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“…The displacements of the tungsten atoms are very small when WO 3 undergoes a phase transition, which leads to minor changes in the x-ray pattern. However, only a limited number of Raman studies on sintering WO 3 ceramics have been performed, 14,23 to our knowledge. In particular, an investigation of the phase transitions in WO 3 ceramics below room temperature has not been reported.…”

Section: Introductionmentioning

confidence: 99%

Phase transition in WO₃ microcrystals obtained by sintering process

Filho

Fílho

Freire

et al. 2001

J Raman Spectroscopy

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The vibrational properties of WO 3 ceramics in the 30-300 K temperature range were probed by Raman spectroscopy. Starting with WO 3 ceramics at room temperature presenting monoclinic (V) and triclinic (VI) mixed phases, structural transitions related to decreasing temperature were observed. At low temperatures a monoclinic (VII) and a new mixed phase were observed, the former characteristic of WO 3 bulk and the latter associated to microcrystals. The analysis of the spectra indicated that the new phase develops gradually and it comes mainly from the monoclinic (V) phase.

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Coexistence of triclinic and monoclinic phases in WO3 ceramics

Cited by 61 publications

References 13 publications

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Preparation, Characterization, and Evaluation of Humidity-Dependent Electrical Properties of Undoped and Niobium Oxide-Doped TiO₂ : WO₃ Mixed Powders

Phase transition in WO₃ microcrystals obtained by sintering process

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Coexistence of triclinic and monoclinic phases in WO3 ceramics

Cited by 61 publications

References 13 publications

Honey-Comb Structured WO3/TiO2Thin Films with Improved Electrochromic Properties

Honey-Comb Structured WO3/TiO2Thin Films with Improved Electrochromic Properties

Preparation, Characterization, and Evaluation of Humidity-Dependent Electrical Properties of Undoped and Niobium Oxide-Doped TiO2 : WO3 Mixed Powders

Phase transition in WO3 microcrystals obtained by sintering process

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Product

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About

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Honey-Comb Structured WO₃/TiO₂Thin Films with Improved Electrochromic Properties

Preparation, Characterization, and Evaluation of Humidity-Dependent Electrical Properties of Undoped and Niobium Oxide-Doped TiO₂ : WO₃ Mixed Powders

Phase transition in WO₃ microcrystals obtained by sintering process