Local geometric and electronic structures of gasochromic VOx films

Abstract

VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V(4+) and V(5+) valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 °C, and the lamellar structure was eliminated at 400 °C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V(5+) and V(3+). Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H2 gas sensors.

Effect of post-annealing on structural and electrochromic properties of Mo-doped V2O5 thin films

“…The electrochromic (EC) thin films have drawn great attentions over the past 50 years due to their numerous applications such as smart windows, auto rearview mirrors, large-area displays, color glasses, and space shuttles [1][2][3][4][5]. In particular, electrochromic material-based devices have multiple advantages such as low-voltage operation, lowenergy consumption, low-carbon green, and memory effect without power supply.…”

Mechanism of Electrochemical Deposition and Coloration of Electrochromic V2O5 Nano Thin Films: an In Situ X-Ray Spectroscopy Study

“…The above features are highly sensitive to the effective valence state of the vanadium and the chemical environment surrounding the vanadium site [22, 23]. The V 2 O 5 thin films deposited for 20 s are most likely in the form of V 5+ with octahedral symmetry [19, 23]. Examination of the spectra with deposition time reveals that the edge energy shifted to increased values (inset of Fig.…”

“…Examination of the spectra with deposition time reveals that the edge energy shifted to increased values (inset of Fig. 3a), suggesting that vanadium is most likely in the form of V 5+ with pyramid symmetry in the V 2 O 5 electrode deposited for 40 and 60 s [19, 24]. In addition to the shift in edge energy, the intensity of the pre-edge peak also increases, suggesting an increase in the distortion of the VO 5 square pyramid with increasing deposition time [25].…”

“…Numerous studies on the application of V 2 O 5 in energy-saving (smart windows [13]) or energy storage devices (batteries/supercapacitors [14]) have reported various synthesis methods [15], electrochemical properties, and photocatalytic performances [16]. Several studies have also demonstrated the importance of electronic structure characterization [17–19]. Eyert et al [17] indicated that octahedral distortions enhance the optical band gap.…”

Dual phase titanium alloy hot forging process design: experiments and numerical modeling

“…Therefore, smart coatings based on electrochromism [6][7][8][9][10], thermochromism [11][12][13][14][15][16][17][18][19], gasochromism [20][21][22] and photochromism [23][24][25][26] have been widely studied for energy efficient coatings. Thermochromic smart coatings can modulate near-infrared radiation from transmissive to opaque in response to the environmental temperature from low to high, which does not require extra stimuli and can save more energy consumption.…”