Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

Ghedira, M.; Vincent, H.; Marezio, M.; Launay, J.C.

doi:10.1016/0022-4596(77)90020-2

Cited by 81 publications

(63 citation statements)

References 17 publications

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“…This phase diagram differs slightly from that given by other authors, which fact has been attributed to differences in sample preparation and stoichiometry [20,64]. Lateron, a similar phase diagram was reported for V 1−x Al x O 2 by Ghedira et al [65,66]. According to Fig.…”

Section: The M 2 Phasesupporting

confidence: 65%

“…The M 2 to T transition was thus viewed as a bonding or dimerization transition of a linear Heisenberg chain. This interpretation was confirmed by the observed decrease of the magnetic susceptibility at the transition, which is accompanied by an increase of the electrical conductivity by a factor of two [66]. From the existence of well localized 3d electrons at the V 4+ sites, Pouget et al concluded that the results should be interpreted in terms of a Mott-Hubbard-type picture.…”

Section: The M 2 Phasementioning

confidence: 88%

“…The parameters given by Marezio et al, which will be used in the calculations below, are listed in Table 5. Ghedira et al, who performed single crystal measurements on VO 2 doped with 1.5% of aluminum, also found a simple monoclinic lattice with lattice constants a M2 = 9.060Å, b M2 = 5.800Å, c M2 = 4.5217Å, monoclinic angle β M2 = 91.85 • , and the atomic positions listed in Table 6 [65,66]. The striking close agreement of both data sets supports the interpretation of the M 2 phase as a metastable modification of the M 1 phase, which hardly depends on the dopant and the amount of doping.…”

Section: The M 1 Structurementioning

confidence: 95%

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

2002

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The results of first principles electronic structure calculations for the metallic rutile and the insulating monoclinic M1 phase of vanadium dioxide are presented. In addition, the insulating M2 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 t2g orbitals, which fall into the one-dimensional d band, and the isotropically dispersing e π g bands. Hybridization of both types of bands is weak. In the M1 phase splitting of the d band due to metal-metal dimerization and upshift of the e π g 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 d band in an embedding background of e π g electrons. In the M2 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 d 1 compounds, the d and e π g bands can be completely separated, which leads to the observed metal-insulator transitions.

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Section: The M 2 Phasesupporting

confidence: 65%

Section: The M 2 Phasementioning

confidence: 88%

Section: The M 1 Structurementioning

confidence: 95%

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

2002

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“…This was seen when VO 2 was doped with Cr 3+ and Al 3+ +, where M2 was stabilized because of the presence of V 5+ which in turn, promoted hole doping. 14,31 But in contrast with W doping, W 6+ substitutes for V 4+ , adds two electrons for each W atom to the system, disrupting V 4+ -V 4+ and creates V 3+ . Evidences of the addition of electrons to the system can be seen from our room temperature Hall-effect measurements and our activation energy analysis.…”

Section: Resultsmentioning

confidence: 99%

Effect of W addition on the electrical switching of VO2 thin films

Rajeswaran

Umarji

2016

AIP Advances

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Vanadium Oxide has been a frontrunner in the field of oxide electronics because of its metal-insulator transition (MIT). The interplay of different structures of VO2 has played a crucial role in deciding the magnitude of the first order MIT. Substitution doping has been found to introduce different polymorphs of VO2. Hence the role of substitution doping in stabilizing the competing phases of VO2 in the thin film form remains underexplored. Consequently there have been reports both discounting and approving such a stabilization of competing phases in VO2. It is reported in the literature that the bandwidth of the hysteresis and transition temperature of VO2 can be tuned by substitutional doping of VO2 with W. In this work, we have adopted a novel technique called, Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) to deposit VO2 and W- doped VO2 as thin films. XRD and Raman spectroscopy were used to investigate the role of tungsten on the structure of VO2 thin films. Morphology of the thin films was found to be consisting of globular and porous nanoparticles of size ∼ 20nm. Transition temperature decreased with the addition of W. We found that for 2.0 at % W doping in VO2, the transition temperature has reduced from 68 o C to 25 o C. It is noted that W-doping in the process of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration.

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“…Such effects can be especially acute for “rugged” energy landscapes characterized by a series of closely related polymorphs. For instance, the introduction of Al and Cr on the vanadium sublattice of VO 2 stabilizes the M 2 polymorph, whereas substitutional W‐ and Mo‐doping on the vanadium sublattice preferentially stabilizes the R polymorph over the M 1 polymorph even rendering the former metallic phase accessible at room temperature . Interstitial B‐doping of VO 2 similarly stabilizes the R polymorph over the M 1 polymorph, thereby strongly depressing the characteristic MIT temperature, whereas in contrast, interstitial H incorporation stabilizes two distinct orthorhombic phases, O 1 and O 2 .…”

Section: Resultsmentioning

confidence: 99%

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO₂ upon Iridium Doping

Braham

Andrews

Alivio

et al. 2018

Physica Status Solidi (a)

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Metastable compounds accessible through kinetic stabilization or under conditions of constrained equilibrium represent a richly varied landscape of structures, properties, and function that are oftentimes entirely inaccessible in thermodynamic minima. The multiple redox states of vanadium and the ability to modulate the connectivity of vanadium and oxygen atoms yields a rich diversity of structures for binary vanadium oxides. Here, it is demonstrated that an orthorhombic quasi‐1D polymorph of VO2, characterized by extended tunnels with a rectangular cross‐section, can be stabilized through the substitutional doping of iridium on the vanadium sublattice. The obtained structure is considerably distorted from a previously reported paramontroseite mineral phase. The metastable phase is obtained in nanoplatelet form and is stable with respect to the energetically proximate monoclinic/rutile thermodynamic minima up to a temperature of 350 °C. The open framework structure and the accessibility of multiple redox states at the vanadium center suggests that the polymorph could potentially serve as an intercalation host. Beyond the solubility limit of iridium on the vanadium sublattice (1.28–3.15 at.% depending on the precursor concentration), metallic Ir nanocrystals are found to be homogeneously dispersed on the surfaces of the nanoplatelets indicating a strong interaction between the metal nanocrystals and oxide lattice.

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Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

Cited by 81 publications

References 17 publications

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

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

Effect of W addition on the electrical switching of VO2 thin films

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO₂ upon Iridium Doping

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Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

Cited by 81 publications

References 17 publications

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

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

Effect of W addition on the electrical switching of VO2 thin films

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO2 upon Iridium Doping

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Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO₂ upon Iridium Doping