Electronic Structure Of VO2 Research Articles

Reversible Switching Between Microwave Absorption and EMI Shielding of VO2 Composite Foam.

Developing lightweight composite with reversible switching between microwave (MW) absorption and electromagnetic interference (EMI) shielding is promising yet remains highly challenging due to the completely inconsistent attenuation mechanism for electromagnetic (EM) radiation. Here, a lightweight vanadium dioxide/expanded polymer microsphere composites foam (VO2/EPM) is designed and fabricated with porous structures and 3D VO2 interconnection, which possesses reversible switching function between MW absorption and EMI shielding under thermal stimulation. The VO2/EPM exhibits MW absorption with a broad effective absorption bandwidth of 3.25GHz at room temperature (25 °C), while provides EMI shielding of 23.1dB at moderately high temperature (100 °C). This reversible switching performance relies on the porous structure and tunability of electrical conductivity, complex permittivity, and impedance matching, which are substantially induced by the convertible crystal structure and electronic structure of VO2. Finite element simulation is employed to qualitatively investigate the change in interaction between EM waves and VO2/EPM before and after the phase transition. Moreover, the application of VO2/EPM is demonstrated with a reversible switching function in controlling wireless transmission on/off, showcasing its excellent cycling stability. This kind of smart material with a reversible switching function shows great potential in next-generation electronic devices.

Transport behavior and electronic structure of phase pure VO2 thin films grown on c-plane sapphire under different O2 partial pressure

We grew highly textured phase pure VO2 thin films on c-plane Al2O3 substrates with different oxygen partial pressure. X-ray absorption and photoemission spectroscopy confirm the identical valence state of vanadium ions despite the different oxygen pressure during the deposition. As the O2 flow rate increases, the [010] lattice parameter for monoclinic VO2 was reduced and coincidently distinctive changes in the metal-semiconductor transition (MST) and transport behaviors were observed despite the identical valence state of vanadium in these samples. We discuss the effect of the oxygen partial pressure on the monoclinic structure and electronic structure of VO2, and consequently the MST.

Cluster model calculations with nonlocal screening channels of metallic and insulatingVO2

We studied the changes in the electronic structure of VO2 across the metal-insulator transition. The main technique was cluster model calculations with non-local screening channels. The calculation included a screening from a coherent state at the Fermi level in the metallic phase, and a screening from a Hubbard charge fluctuation within the V-V dimmer in the insulating phase. The calculation results are compared to previous photoemission and X-ray absorption spectra. The coherent feature at the Fermi level in the metallic phase is due to the coherent screening. But the Hubbard screened state in the insulating phase appears at higher energies opening the band gap. The changes in the electronic structure of VO2 are thus related to the non-local screening channels.

A model for electronic structure of VO2

Abstract In order to examine the metal-insulator transition in vanadium dioxide (VO2) a number of numerical calculations have been made which attempt to place a chemical emphasis on the understanding of this phenomenon. Angular overlap model (ADM) calculations have been applied to VO6 8- octahedra in the distorted and rutile phases to show the energies and characters of the perturbed V 3d orbitals. These results have then been used to construct Coulson-Fischer-type wavefunctions to model the effects of V-V bonding along the c axis. Calculations have been made on both V-V dimers and V-V chains, using complete neglect of differential overlap (CNDO)- and intermediate neglect of differential overlap (INDO)-type approximations to show the effects on the occupation of the V 3d orbitals of changing the lattice and electron correlation.

The electronic structure of VO2+, CrO3+, and MoO3+ complexes

The electronic structure of VO2+, CrO3+, and MoO3+ complexes