Thin Films of Bismuth Vanadates with Modifiable Conduction Properties

Abstract

Thin films of bismuth vanadates are deposited by chemical vapor deposition (CVD) on α-Al2O3 substrates using an O2 atmosphere and vanadyl(IV) acetylacetonate and triphenylbismuth as precursors. The microstructure of the samples is studied by XRD and Raman spectroscopy and their chemical composition is investigated by XPS and SIMS. AFM is used to analyze the surface morphology of the samples. All the samples show a nonohmic behavior beyond a threshold voltage, V th, which is linearly dependent on the V4+/V5+ ratio. Impedance spectroscopy measurements indicate that the obtained samples are oxide ion conductors at room temperature and that the mechanism of ion conduction occurs by means of hopping between vacancies. Furthermore, ferroelectric−paraelectric transitions take place in the materials at low temperatures.

Reactive Sputtering of Bismuth Vanadate Photoanodes for Solar Water Splitting

“…We did not detect the additional bands expected for either the Raman mode of the α-phase Bi 2 O 3 material (306 cm −1 ) or the ferroelectric Bi 2 VO 5.5 (850 cm −1 ), as have been reported previously for strongly offstoichiometric films. 30 For the V-rich film, we observe additional weak but sharp lines at 400 and 980 cm −1 , which become even more intense in films with lower Bi/V ratios. These peaks match the frequencies of the Raman-active vibrational modes of V 2 O 5 and are consistent with the wirelike features in Figure 2b.…”

Thermochromic Coatings for Intelligent Architectural Glazing

“…Vanadyl acetylacetonate, [VO(acac) 2 ], has been used to prepare the meta-stable VO 2 (B), which can be converted to the tetragonal phase by annealing in argon at 500 ºC [57][58]. Vanadyl precursors have also been used in a CVD method to prepare various vanadium oxide thin films including vanadium (IV) oxide [59]. The precursors used in these studies are generally expensive and require a post-deposition reduction process to form vanadium (IV) oxide thin films.…”

“…As anticipated, thinner films have higher transmittance in the visible part of the spectrum and show a larger change on moving through the transition temperature. Ideally a glazing product will have a visible transmittance of at least 55% [59].…”

The Growth of Thermochromic VO2 Films on Glass by Atmospheric-Pressure CVD: A Comparative Study of Precursors, CVD Methodology, and Substrates

“…[15] The vanadyl compound VO(acac) 2 has been used to prepare metastable VO 2 , which was then converted to the tetragonal phase VO 2 by annealing in argon at 500°C. [16,17] Various other vanadyl complexes have also been used for the deposition of VO 2 films. [18] Previous studies from our laboratories, [19,20,21] in collaboration with the group of Parkin (University College London), have also focused on the CVD growth of VO 2 thin films on glass using APCVD methods.…”