Magnetismus, Leitfähigkeit und Reflexionsspektren von Vanadindioxyd und Vanadindioxyd–Titandioxyd‐Mischkristallen

Rüdorff, W.; Walter, G.; Stadler, Jens M.

doi:10.1002/zaac.19582970102

Cited by 70 publications

(16 citation statements)

References 14 publications

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“…The substitutions of most elements for V are limited below 20 mol%, above which either other phases are stabilized or conventional twophase mixtures are obtained. In the Ti substitution system V 1-x Ti x O 2 , in contrast, it was reported that complete SSs could be prepared in polycrystalline samples or thin films [14,49,51,58]. In a later study on the single crystal growth, however, the presence of complete SSs was questioned because single crystals were obtained only for x > 0.8 even from nominal compositions of x > 0.5 [52].…”

Section: Spinodal Decompositionmentioning

confidence: 98%

“…There are two classes of substitution systems V 1-x M x O 2 : T MI increases slightly for M = Cr 3+ [19,[44][45][46], Al 3+ [47], Fe 3+ [48], and Ti 4+ [13,[49][50][51][52], while it decreases rapidly for M = Nb 5+ [49,53], Mo 6+ [54], and W 6+ [55,56]. In terms of a simple electron counting with n being the number of excess electrons per formula unit, a Cr 3+ ion gives one hole and two electrons so that n = x in total, while a Ti 4+ ion introduces one hole; n = -x.…”

Section: Substitution Effects In Vomentioning

confidence: 99%

“…A true mechanism of the MIT in VO 2 should give reasonable explanations to these complex substitution effects. [13,50], Cr 3+ [44,45], Nb 5+ [49,53], Mo 6+ [54], and W 6+ [55,56]. The horizontal axis refers to the number of excess electrons per formula unit in the simple electron counting scheme: n = -x (M = Ti …”

Section: Substitution Effects In Vomentioning

confidence: 99%

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Structural instability of the rutile compounds and its relevance to the metal–insulator transition of VO2

Hiroi

2015

Progress in Solid State Chemistry

103

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The metal-insulator transition (MIT) of VO 2 is discussed with particular emphasis on the structural instability of the rutile compounds toward dimerization. Ti substitution experiments reveal that the MIT is robust up to 20% Ti substitutions and occurs even in extremely thin V-rich lamellas in spinodally decomposed TiO 2 -VO 2 composites, indicating that the MIT is insensitive to hole doping and essentially takes on a local character. These observations suggest that either electron correlation in the Mott-Hubbard sense or Peierls (Fermi-surface) instability plays a minor role on the MIT. Through a broad perspective of crystal chemistry on the rutile-related compounds, it is noted that VO 2 and another MIT compound NbO 2 in the family eventually lie just near the borderline between the two structural groups with the regular rutile structure and the distorted structures characterized by the formation of dimers with direct metal-metal bonding. It is also shown that the two compounds of the rutile form do not follow the general trends in structure observed for the other rutile compounds, giving clear evidence of an inherent structural instability present in the two compounds. The MITs of VO 2 and NbO 2 are natural consequences of structural transitions between the two groups, as all the d electrons are trapped in the bonding molecular orbitals of dimers at low temperatures. Such dimer crystals are ubiquitously found in early transition metal compounds having chain-like structures, such as MoBr 3 , NbCl 4 , Ti 4 O 7 , and V 4 O 7 , the latter two of which also exhibit MITs probably of the same origin. In a broader sense, the dimer crystal is a kind of "molecular orbital crystals" in which virtual molecules made of transition metal atoms with partially-filled t 2g shells, such as dimers, trimers or larger ones, are generated by metal-metal bonding and are embedded into edge-or face-sharing octahedron networks of various kinds. The molecular orbital crystallization opens a natural route to stabilization of unpaired t 2g electrons in crystals.2

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Section: Spinodal Decompositionmentioning

confidence: 98%

Section: Substitution Effects In Vomentioning

confidence: 99%

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Structural instability of the rutile compounds and its relevance to the metal–insulator transition of VO2

Hiroi

2015

Progress in Solid State Chemistry

103

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“…Vanadium dioxide (VO 2 ) is a transition metal compound with tremendous potential for technological applications, essentially in reason of its nearly room temperature metal-to-insulator transition [1][2][3][4][5][6][7][8][9][10]. Over the years, VO 2 has been subject to an intense investigation, which dates back to the first decades of the last century [11][12][13][14][15][16][17][18][19][20], but that is yet alive [21][22][23] and, to some extent, debated [24][25][26][27][28][29][30]. At the critical temperature T c ∼ 340 K and ambient pressure, VO 2 undergoes a first-order transition from a metal (T > T c ) to an insulator (T < T c ) [31,32], both phases being paramagnetic [33][34][35].…”

Section: Introductionmentioning

confidence: 99%

Unraveling the Mott-Peierls intrigue in vanadium dioxide

Grandi

Amaricci

Fabrizio

2020

Phys. Rev. Research

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Vanadium dioxide is one of the most studied strongly correlated materials. Nonetheless, the intertwining between electronic correlation and lattice effects has precluded a comprehensive description of the rutile metal to monoclinic insulator transition, in turn triggering a longstanding "the chicken or the egg" debate about which comes first, the Mott localisation or the Peierls distortion. Here, we show that this problem is in fact ill-posed: the electronic correlations and the lattice vibrations conspire to stabilise the monoclinic insulator, and so they must be treated on equal footing not to miss relevant pieces of the VO2 physics. Specifically, we design a minimal model for VO2 that includes all the important physical ingredients: the electronic correlations, the multi-orbital character, and the two components antiferrodistortive mode that condenses in the monoclinic insulator. We solve this model by dynamical mean-field theory within the adiabatic Born-Oppenheimer approximation. Consistently with the first-order character of the metal-insulator transition, the Born-Oppenheimer potential has a rich landscape, with minima corresponding to the undistorted phase and to the four equivalent distorted ones, and which translates into an equally rich thermodynamics that we uncover by the Monte Carlo method. Remarkably, we find that a distorted metal phase intrudes between the low-temperature distorted insulator and high-temperature undistorted metal, which sheds new light on the debated experimental evidence of a monoclinic metallic phase.

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“…Surface electronic states are associated with defects produced by Ar+ bombardment of TiO, crystals [17] and Ar+ ion bombardment preferentially removes oxygen from the TiO, surface [18, 191. In this work the results of ESCA, optical absorption, electrical and ESR measurements on the TiO, and V,Til-,O, crystals wit,h different degree of reduction are presented and the relation between the electronic structure of these crystals and the conduction mechanism is discussed. [20]. Single crystals in this system were prepared by Verneuil's flame fusion method [21].…”

Section: Introductionmentioning

confidence: 99%

Study of electronic structure of reduced TiO₂ and V_xTi_1−xO₂ crystals by ESCA and optical absorption

Sakata¹

1983

Physica Status Solidi (b)

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An analysis is made of optical absorption spectra and electron spectroscopy for chemical analysis (ESCA) on pure TiO,, reduced TiO,, and V,Til -z02. It is found that in the reduced TiO,, the Ti ion takes the variable valence states, Ti4+, TiS+, and Ti2+, and they form a broad donor band, which overlaps with the conduction band originating from Ti4s levels. 3 d -4~ mixing results in a large change of the conductivity of TiO, from insulator to metal depending upon the degree of reduction. I n TiO, doped with V, which behaves like a free ion, the excess 3d electrons of the V ions form impurity level just above the 02p valence band. In the reduced V,Til -,O,, four different valence states, Ti4+, Ti3+, Ti2+, and V 4 ' , are found and this accounts for the narrow optical gap of this material.Es wird eine Analyse der optischen Absorptionsspektren und der ESCA-Spektren an reinem TiO,, reduziertem TiO, und V,Til-,O, durchgefiihrt. Es wird gefunden, daS im reduzierten TiO, die Ti-Ionen variable Valenzzustknde Ti4+, Ti3+, und Ti2+ annehmen und ein breites Donatorband bilden, das mit dem von den Tils-Zustanden stammenden Leitungsband uberlappt. 3d-4~-Mischung ergibt eine starke Anderung der Leitfahigkeit von TiO, vom Isolator zum Metal1 abhiingig vom Reduktionsgrad. Im TiO,, das mit V dotiert ist, was sich wie ein freies Ion betriigt, bilden die uberschiissigen 3d-Elektronen des V-Ions Storstelleniveaus etwas oberhalb des O2p-Valenzbandes. Im reduzierten V,Til -%O, werden vier nnterschiedliche Valenzzustiinde Ti4+, TiS+, Ti2+ und V4+ gefunden, was die schmale optische Bandliicke dieses Materials erkliirt.

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Magnetismus, Leitfähigkeit und Reflexionsspektren von Vanadindioxyd und Vanadindioxyd–Titandioxyd‐Mischkristallen

Cited by 70 publications

References 14 publications

Structural instability of the rutile compounds and its relevance to the metal–insulator transition of VO2

Structural instability of the rutile compounds and its relevance to the metal–insulator transition of VO2

Unraveling the Mott-Peierls intrigue in vanadium dioxide

Study of electronic structure of reduced TiO₂ and V_xTi_1−xO₂ crystals by ESCA and optical absorption

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Magnetismus, Leitfähigkeit und Reflexionsspektren von Vanadindioxyd und Vanadindioxyd–Titandioxyd‐Mischkristallen

Cited by 70 publications

References 14 publications

Structural instability of the rutile compounds and its relevance to the metal–insulator transition of VO2

Structural instability of the rutile compounds and its relevance to the metal–insulator transition of VO2

Unraveling the Mott-Peierls intrigue in vanadium dioxide

Study of electronic structure of reduced TiO2 and VxTi1−xO2 crystals by ESCA and optical absorption

Contact Info

Product

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About

Study of electronic structure of reduced TiO₂ and V_xTi_1−xO₂ crystals by ESCA and optical absorption