The metal‐insulator transitions of VO₂: A band theoretical approach

Abstract

The results of first principles electronic structure calculations for the metallic rutile and the insulating monoclinic phase of vanadium dioxide are presented. In addition, the insulating phase is investigated for the first time. The density functional calculations allow for a consistent understanding of all three phases. In the rutile phase metallic conductivity is carried by metal orbitals, which fall into the one‐dimensional band, and the isotropically dispersing bands. Hybridization of both types of bands is weak. In the phase splitting of the band due to metal‐metal dimerization and upshift of the bands due to increased p‐d overlap lead to an effective separation of both types of bands. Despite incomplete opening of the optical band gap due to the shortcomings of the local density approximation, the metal‐insulator transition can be understood as a Peierls‐like instability of the band in an embedding background of electrons. In the phase, the metal‐insulator transition arises as a combined embedded Peierls‐like and antiferromagnetic instability. The results for VO2 fit into the general scenario of an instability of the rutile‐type transition‐metal dioxides at the beginning of the d series towards dimerization or antiferromagnetic ordering within the characteristic metal chains. This scenario was successfully applied before to MoO2 and NbO2. In the compounds, the and bands can be completely separated, which leads to the observed metal‐insulator transitions.

Nanoscale Control of Oxygen Defects and Metal–Insulator Transition in Epitaxial Vanadium Dioxides

“…The calculated bandgap of the M1 phase increases from 0.007 eV at U = 0 to 0.83 eV at U = U opt , close to the experimentally measured optical gap (0.6 eV). 41,42 We incorporated a single oxygen vacancy in a 48-atom supercell of VO 2 in the M1 phase, corresponding to a vacancy concentration of 3.125%. For a neutral vacancy, the standard semilocal PBE functional gives rise to a fully delocalized charge density, as shown in Figure 5a.…”

Polarized Tip-Enhanced Raman Spectroscopy in Understanding Metal-to-Insulator and Structural Phase Transition in VO2

“…9 The T phase is intermediate between the M1 and M2 phases. 10 The M2 phase, composed by one set of equally spaced V chains, is defined as a Mott−Hubbard insulator, and superposition of two M2-type lattice distortions may be considered as the M1 phase. 8,11,12 As the MIT is generally accompanied by a SPT in VO 2 , the chicken−egg controversy remains, whether the dynamical electron (spin)−phonon coupling or strong electron−electron correlation triggers the MIT.…”

Influences of W Content on the Phase Transformation Properties and the Associated Stress Change in Thin Film Substrate Combinations Studied by Fabrication and Characterization of Thin Film V1–xWxO2 Materials Libraries

“…V atoms pair along the rutile c axis in zigzag type, exhibiting alternative distances of 0.312 and 0.265 nm. 6 Along the transformation from M phase to R phase, the unit cell of VO 2 expands by ∼0.32% (one unit cell of M phase consists of two unit cells of R phase) and the area for (011) M and (110) R planes is decreased by 1.7%, resulting in a strain of up to 1% along the rutile c axis. Taking the high Young's modulus E of VO 2 (∼140 GPa) into account, this leads to high stresses associated with the phase transformation, which could be used for micro/nanoactuators.…”