FromVO2(B)toVO2

Abstract

The intermediate steps of the phase transition between the metastable monoclinic VO 2 (B) phase and the stable tetragonal rutile VO 2 (R) phase have been studied by in situ electron microscopy. A crystallographic interpretation based on the static concentration waves theory is proposed: as temperature increases, the long-range order in the complex monoclinic VO 2 (B) phase is lost and gradually a first intermediate ill crystallized phase with a drastically reduced symmetry is formed as evidenced from the diffraction patterns. Next, a new tetragonal phase is generated that corresponds to a state where some of the vanadium atoms are now in a disordered state. When annealing inside the microscope, this phase grows out into a superstructure, with coexistence of two possible orientation variants. In all these phases the VO 6 octahedra remain virtually parallel, but for the final transition around 450°C into the rutile stable phase, half of the octahedra have to reorient; the transition therefore has the aspects of a reconstructive one as is evident from the in situ experiment.

Nanothermochromics: Calculations for VO2 nanoparticles in dielectric hosts show much improved luminous transmittance and solar energy transmittance modulation

“…97 Nanorods ͑nanoribbons, nanobelts͒ of this material have been prepared by wet chemical techniques in numerous studies 95,[98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115] and the capability for electrochemical lithium insertion has been investigated. VO 2 ͑B͒ is not in itself a good thermochromic material but it can be transformed to thermochromic VO 2 via heat treatment, as has been demonstrated for powders 116,117 and nanorods, 103,118 which means that a large body of work made with battery applications in mind is also of relevance for thermochromics.…”

Synthesis and phase transition behavior of w-doped VO2(A) nanorods

“…VO 2 (R) has the highest symmetry in crystallography which contains the most regular oxygenvanadium octahedra aligned along two perpendicular directions on the mutual orientation of the fourfold axis of the oxygen octahedra. The oxygenvanadium octahedra in VO 2 18) it is the nearest one to the average value of the length of VO bond in VO 2 (R). From this point of view, the tungsten could be easily doped into VO 2 (R) then followed by VO 2 (B) and the doping of tungsten into VO 2 (A) would induce greater distortion in the crystal lattice.…”

“…The VO 2 4 , Wako, Japan). All of the chemical reagents used in the experiments were analytical grade without further purification.…”

“…1) The allotropic phases in this system include VO 2 (R), VO 2 (M), VO 2 (B), VO 2 (A) 2) and recently reported VO 2 (C). 3) In particular, a great deal of attention has been paid to rutile type VO 2 (R) for the reason that it undergoes a metal-semiconductor transition (MST) at 68°C 4) which is the closest one to the ambient temperature compared to other compounds having thermochromic behavior ever been found until now.…”

Structure of Flame‐made Vanadia/Titania and Catalytic Behaviour in the Partial Oxidation of o‐Xylene

“…At 7% (w/w) vanadia content, weak reflections corresponding to crystalline VO 2 (B) (diamonds) appeared. Quantification of this phase was not possible, because pure TiO 2 exhibited small and broad diffractions at these angles (14.2 • , 28.4 • , 33.4 • ) which can be attributed to a high-pressure phase TiO 2 (B) with a similar lattice structure and cell size [31]. Nevertheless, the increase in peak intensities at these angles with increasing V 2 O 5 content may indicate the presence of a small fraction of crystalline VO 2 (B), at least for V 2 O 5 content >7% (w/w) for the LE-FSP-made catalysts.…”