A Powder Neutron Diffraction Study of Semiconducting and Metallic Niobium Dioxide

Bolzan, Adrian A.; Fong, Celesta; Kennedy, Brendan J.; Howard, Christopher

doi:10.1006/jssc.1994.1334

Cited by 81 publications

(61 citation statements)

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“…Figure 11 plots the x coordinate of anions as a function of c/a for the undistorted rutile compounds; similar plots have already been given [80,81,90]. Most data except for NbO 2 were obtained at around room temperature, whereas the NbO 2 data was obtained at 1273 K above the T MI [91]. Although there is a positive temperature dependence for c/a (see Fig.…”

Section: Structural Instability In the Rutile Compoundssupporting

confidence: 57%

“…11 that the x values of the AO 2 compounds are rather constant at around 0.305, insensitive to the A element as well as the c/a ratio. [67], and Bolzan et al [91], clearly indicating that the two compounds already suffer a certain instability on the verge of the stability range of the rutile type [35,74,91]. 2 , plotted in Fig.…”

Section: Structural Instability In the Rutile Compoundsmentioning

confidence: 79%

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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

100

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: Structural Instability In the Rutile Compoundssupporting

confidence: 57%

Section: Structural Instability In the Rutile Compoundsmentioning

confidence: 79%

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

Hiroi

2015

Progress in Solid State Chemistry

100

103

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“…Among these materials is NbO 2 which exhibits one of the highest MIT temperatures of 1081K [16][17], accompanied by a structural transition from a distorted rutile (low temperature) to a rutile structure (high temperature phase). The low temperature NbO 2 has a tetragonal unit cell (space group I4 1 /a, a T = 13.702 Å and c T = 5.985 Å [16]), whereas the high temperature phase is described by a rutile unit cell (space group P4 2 /mnm, a = 4.846 Å and c = 3.032 Å [16]). …”

Section: Introductionmentioning

confidence: 99%

Preparation, characterization, and electrical properties of epitaxial NbO₂thin film lateral devices

Joshi¹,

Senty²,

Borisov³

et al. 2015

J. Phys. D: Appl. Phys.

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Epitaxial NbO 2 (110) films, 20 nm thick, were grown by pulsed laser deposition on Al 2 O 3 (0001) substrates. The Ar/O 2 total pressure during growth was varied to demonstrate the gradual transformation between NbO 2 and Nb 2 O 5 phases, which was verified using x-ray diffraction, x-ray photoelectron spectroscopy, and optical absorption measurements. Electric resistance threshold switching characteristics were studied in a lateral geometry using interdigitated Pt top electrodes in order to preserve the epitaxial crystalline quality of the films.Volatile and reversible transitions between high and low resistance states were observed in epitaxial NbO 2 films, while irreversible transitions were found in case of Nb 2 O 5 phase. Electric field pulsed current measurements confirmed thermally-induced threshold switching.

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“…Nb is a well known candidate in terms of its ease of oxidation. However, its multiple valence states could produce multiple NbO x species with electrical properties that range from metallic, to semiconducting, to insulating [10]. This also typically leads to a nonuniform surface oxide layer, which is not suitable for Josephson tunnel barriers.…”

Section: Introductionmentioning

confidence: 99%

Fabrication of $\hbox{Nb/Al}_{2}\hbox{O}_{3}/\hbox{Nb}$ Josephson Junctions Using In Situ Magnetron Sputtering and Atomic Layer Deposition

Elliot

Wille

et al. 2013

IEEE Trans. Appl. Supercond.

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Abstract-Atomic layer deposition (ALD) provides a promising approach for deposition of ultrathin low-defectdensity tunnel barriers, and it has been implemented in a highvacuum magnetron sputtering system for in situ deposition of ALD-Al 2 O 3 tunnel barriers in superconductor-insulatorsuperconductor (SIS) Josephson junctions. A smooth ALD-Al 2 O 3 barrier layer was grown on a Al-wetted Nb bottom electrode and was followed with a top Nb electrode growth using sputtering. Preliminary low temperature measurements of current-voltage characteristics (IVC) of the Josephson junctions made from these trilayers confirmed the integrity of the ALD-Al 2 O 3 barrier layer. However, the I c R N product of the junctions is much smaller than the value expected from the Ambegaokar-Baratoff formula suggesting a significant pair-breaking mechanism at the interfaces.

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A Powder Neutron Diffraction Study of Semiconducting and Metallic Niobium Dioxide

Cited by 81 publications

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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

Preparation, characterization, and electrical properties of epitaxial NbO₂thin film lateral devices

Fabrication of $\hbox{Nb/Al}_{2}\hbox{O}_{3}/\hbox{Nb}$ Josephson Junctions Using In Situ Magnetron Sputtering and Atomic Layer Deposition

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A Powder Neutron Diffraction Study of Semiconducting and Metallic Niobium Dioxide

Cited by 81 publications

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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

Preparation, characterization, and electrical properties of epitaxial NbO2thin film lateral devices

Fabrication of $\hbox{Nb/Al}_{2}\hbox{O}_{3}/\hbox{Nb}$ Josephson Junctions Using In Situ Magnetron Sputtering and Atomic Layer Deposition

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Preparation, characterization, and electrical properties of epitaxial NbO₂thin film lateral devices