Studies on Vanadium Oxides. I. Phase Analysis.

Andersson, Georg; Paju, Julius; Lang, Wendy; Berndt, W.

doi:10.3891/acta.chem.scand.08-1599

Cited by 295 publications

(94 citation statements)

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“…In addition, there is another related family of compounds that exhibit MITs; the Magnéli phases, Ti n O 2n-1 and V n O 2n-1 [32][33][34][35], which exist between TiO 2 (VO 2 ) and Ti 2 O 3 (V 2 O 3 ) with mixed-valence metal ions. The structures of the Magnéli phases are obtained by periodically introducing a stacking fault with an extra plane of metal atoms (called a shear plane) into the mother rutile structure; the composition is decided by the periodicity.…”

Section: Mits In Vo 2 and Related Compoundsmentioning

confidence: 99%

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: Mits In Vo 2 and Related Compoundsmentioning

confidence: 99%

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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“…(η = 4,5.. .9), and Vn02n-i (Magneli 1953, I960;Andersson, 1954). In these oxides the octahedral coordination about the metal atoms is preserved but, at regular spacings, edge sharing is added to corner sharing in the molybdenum oxides, or face sharing to edge sharing in the rutile structure.…”

Section: Problem 2 Are Grossly Nonstoichiometric Compounds Thermodynmentioning

confidence: 99%

“…An alternative way of changing the cationanion ratio of a structure without a radical change in the coordination environment of any atom (though at the cost of increasing the repulsive terms in the lattice energy sum) is found in the remarkable series of homologous oxides of molybdenum, titanium, and vanadium, discovered by Magnéli and his collaborators (2,27,28):…”

Section: Problem 2 Are Grossly Nonstoichiometric Compounds Thermodynmentioning

confidence: 99%

Current Problems in Nonstoichiometry

Anderson

1963

Advances in Chemistry

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years, in the sense that a fixed composition and a rational formula were taken as the definitive criteria for a compound. As applied to solid compounds, the law was not a generalization from experimental fact.The controversy between Berthollet and Proust was unsatisfactory; it was settled by a dogmatic, but natural, extrapolation of the conclusions drawn by Dalton from the atomic theory. These are inherently valid for discrete molecules. Until physical scientists were ready to think of crystalline inorganic compounds as infinite three-dimensional assemblies of atoms, the stage was not set for reopening this particular aspect of the recurrent problem of the strictly quantized or the statistical and quasicontinuous description of natural phenomena.

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“…Vacancy-induced B1 structures have also been observed in monoxides of other low-valence 3d metals such as TiO and VO by numerous researchers, including Andersson et al 25 TiO and VO maintain a homogeneous B1 structure, even though they include a number of vacancies in the range of TiO 0.64 -TiO 1. 25 25 and VO 0.75 -VO 1.20 , 26 respectively. Cross-sectional TEM results observed from B1 [110] direction are shown in Fig.…”

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confidence: 96%

Nanotwin hardening in a cubic chromium oxide thin film

Suzuki

Nakajima

et al. 2015

APL Materials

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NaCl-type (B1) chromium oxide (CrO) has been expected to have a high hardness value and does not exist as an equilibrium phase. We report a B1-based Cr0.67O thin film with a thickness of 144 nm prepared by pulsed laser deposition as an epitaxial thin film on a MgO single crystal. The thin film contained a number of stacking faults and had a nanotwinned structure composed of B1 with disordered vacancies and corundum structures. The Cr0.67O thin film had a high indentation hardness value of 44 GPa, making it the hardest oxide thin film reported to date.

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Studies on Vanadium Oxides. I. Phase Analysis.

Cited by 295 publications

References 0 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

Current Problems in Nonstoichiometry

Nanotwin hardening in a cubic chromium oxide thin film

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