Phase transitions in tungsten trioxide at low temperatures

Lefkowitz, I.; Dowell, M. B.; Shields, M.

doi:10.1016/0022-4596(75)90267-4

Cited by 60 publications

(11 citation statements)

References 34 publications

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“…(ii) Reasonable electronic [1,8,14] and ionic [1,12,13] conductivities allowing for the diffusion of the electrons balancing the insertion of foreign cations into the structure. In fact, the commercial powders exhibit n-type semiconductivity and show a yellow colour, due to the presence of bulk defects [14].…”

Section: Introductionmentioning

confidence: 99%

“…The colour centres are generally attributed [4] to defects consisting of electron excess charge, localised at the octahedra basic units [WS+O6]. The blue coloration can be induced by different methods such as chemical and electrochemical insertion [3,5] of small cations, UV irradiation [3,6,7] and annealing in vacuum [8]. Treatments inducing some degree of amorphisation of the crystalline structure, like ion beam bombardment [9], promote also the change of electronic distribution in the deformed regions and a consequent modification of its optical properties.…”

Section: Introductionmentioning

confidence: 99%

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Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

Cazzanelli

Mariotto

Vinegoni

et al. 1999

Ionics

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Abstract.The relationship between structural transformations and colour centres creation is discussed for deeply coloured hydrogen tungsten bronzes and for pure WO3 powders, acquiring less intense colour after mechanical treatments of variable duration. A comparative study on coloration is made also for mixed compounds (1-x)WO3.y.xReO 2, where an evidence of a resonance effect for a particular Raman band at 970 cm -1, attributed to the color centres, is observed. Besides, it is found that even moderate milling treatments result in a quite different structural evolution of tungsten trioxide upon cooling.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

Cazzanelli

Mariotto

Vinegoni

et al. 1999

Ionics

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“…Sheet superconductivity at 3 K in twin walls of a non superconducting tetragonal WO 3−x was reported by Aird et al in 1998 [6,7]. For x < 0.3 the Na x WO 3 sodium tungsten bronzes, formed by doping the insulating host WO 3 with Na + ions, are n-type semiconductors.We prepared single crystals in which the surface is doped with Na + ions following the method described in reference [8]. We introduced WO 3 powder, which contains 0.5% atomic concentration of sodium, into platinum tubes 10 cm long and 0.5 cm in inner diameter.…”

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confidence: 99%

“…We prepared single crystals in which the surface is doped with Na + ions following the method described in reference [8]. We introduced WO 3 powder, which contains 0.5% atomic concentration of sodium, into platinum tubes 10 cm long and 0.5 cm in inner diameter.…”

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confidence: 99%

Possible nucleation of a 2D superconducting phase on WO single crystals surface doped with Na

1999

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WO3 crystals with a surface composition of Na0.05WO3 were grown. These crystals exhibit a sharp diamagnetic step in magnetization at 91 K, and a magnetic hysteresis below this temperature. As the temperature is lowered below 100 K in transport measurements, a sharp metal to insulator transition is observed, this is followed by a sharp decrease in the resistivity when the temperature is lowered to about 90 K. When the surface of the crystals was covered by gold the depth of the diamagnetic step had decreased considerably. These results indicate a possible nucleation of a superconducting phase on the surface of these crystals. This is a non cuprate system exhibiting a critical temperature in the HTS range. PACS. 74.70.-b Superconducting materials (excluding high-Tc compounds) -74.20.-z Theories and models of superconducting state -74.60.Ec Mixed state, critical fields, and surface sheathTwo dimensional and quasi 2D superconductivity are common phenomena. The first example goes back to 1963 when Saint-James and de Gennes [1] showed that in an ideal sample with anhomogenous order parameter the nucleation of superconducting regions in decreasing field should always occur near the surface of the sample. For a superconductor of the second kind this implies that in fields H : H 2 < H < H 3 there remains a superconducting sheath on some parts of the sample confined to a thickness of the order of the correlation length ξ. In HTS perovskite cuprates the order parameter is spatially modulated along the c axis as the superconductivity is quasi 2D in character and is confined to the CuO planes coupled by Josephson junctions. A question arises about a possible system in which the structure is modulated in such a way so that superconductivity will develop on the surface only, not a type III superconductivity, and will not propagate into the bulk. In this short paper we suggest that WO 3 single crystals doped on the surface with sodium may constitute such a superconductor. This is a non cuprate system with a critical temperature of 91 K.The 5d-transition-metal oxides WO 3 and Na x WO 3 are similar in electronic structure to 3d oxides. They have nearly the ABO 3 perovskite crystal structure, with the W ions occupying the octahedral B cation sites. In WO 3 the A cation site is vacant, while in Na x WO 3 the Na + ions occupy that site. Stoichiometric WO 3 is an insulator, since the W 5d band is empty; when Na ions are added to WO 3 , they donate their 3s electron to the W 5d band, resulting in bulk metallic behavior for x ≥ 0.3 [2,3]. These materials in tetragonal or hexagonal form exhibit also bulk superconductivity at sub-liquid helium temperature [4,5]. Sheet superconductivity at 3 K in twin walls of a non superconducting tetragonal WO 3−x was reported by Aird et al. in 1998 [6,7]. For x < 0.3 the Na x WO 3 sodium tungsten bronzes, formed by doping the insulating host WO 3 with Na + ions, are n-type semiconductors.We prepared single crystals in which the surface is doped with Na + ions following the method described in reference...

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“…Reduction of the compound results in a small oxygen non-stoichiometry and conducting samples. The stoichiometric material shows thermally activated hopping conductivity with activation energies between 0.15 and 0.27 eV, depending on the crystal quality [8,9,10,11]. At temperatures below 130K there is a change to a regime with much smaller activation energies.…”

Section: Introductionmentioning

confidence: 99%

Effect of pressure on the superconductivity of Rb0.19WO3

Núñez-Regueiro

Freitas

Brusetti

et al. 2013

Solid State Communications

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We have performed electrical resistivity measurements under pressures up to 20GPa between 1 and 300K on monocrystalline hexagonal Rb 0.19 WO 3 . For pressures lower than ~5GPa, we observe a decrease of the metallic-like resistivity at room temperature as well as a small decrease of T c . At this pressure, the resistivity starts to increase slowly up to 10GPa accompanied by a sharper decrease of T c .The resistivity curves above 10GPa denote an activated behaviour and a T c lower than 3K indicating that there is a phase transition that takes place gradually between 5 and 10GPa.We interpret our measurements as the result of structural transformations under high pressure.

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Phase transitions in tungsten trioxide at low temperatures

Cited by 60 publications

References 34 publications

Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

Possible nucleation of a 2D superconducting phase on WO single crystals surface doped with Na

Effect of pressure on the superconductivity of Rb0.19WO3

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