Search results for "niobium"
showing 10 items of 120 documents
Electron-relaxation-mode interaction in BaTiO3:Nb.
1992
Dielectric relaxation was previously reported in ${\mathrm{BaTiO}}_{3}$ and ${\mathrm{BaTiO}}_{3}$:Fe single crystals at radio frequencies [M. Maglione et al., Phys. Rev. B 40, 11 441 (1989)]. We have measured the dielectric dispersion in four ${\mathrm{BaTiO}}_{3}$:Nb samples (${\mathit{x}}_{\mathrm{Nb}}$0.3 at. %) as a function of frequency (10f${10}^{9}$ Hz) and temperature (20T450 K). The electronic conductivity of ${\mathrm{BaTiO}}_{3}$:Nb enhances drastically the relaxation step at all temperatures. In the rhombohedral phase of ${\mathrm{BaTiO}}_{3}$:Nb (T180 K), an unusual slowing down of the relaxation motion is measured. The relaxation time increases to more than ${10}^{\mathrm{\en…
ChemInform Abstract: Nb4Te17I4, a New Pseudo One-Dimensional Solid-State Polytelluride.
2010
The new ternary compound Nb4Te17I4 has been prepared and structurally characterized. It crystallizes in the monoclinic system, space group C2/c with unit-cell parameters a = 16.199(4), b = 8.128(2), c = 27.355(6) A, β = 110.84(2)°, Z = 4. The structure consists of infinite one-dimensional niobium/tellurium chains running parallel to the crystallographic c direction. The chains are separated by iodine atoms. Short and long metal–metal distances alternate in the sequence of three consecutive short bonds ([d ≈ 3.1 – 3.2 A) and one long (d = 4.268 A) metal–metal separation. Each Nb atom is eight-coordinate. The composition of the chain is ∞11[(Nb5+)2(Nb4+)2(Te22−)4(Te32−)3(I−)4].
Critical-state effects on microwave losses in type-II superconductors
2006
We discuss the microwave energy losses in superconductors in the critical state. The field-induced variations of the surface resistance are determined, in the framework of the Coffey and Clem model, by taking into account the distribution of the vortex magnetic field inside the sample. It is shown that the effects of the critical state cannot generally be disregarded to account for the experimental data. Results obtained in bulk niobium at low temperatures are quantitatively justified.
Enhanced Heterogeneous Catalytic Conversion of Furfuryl Alcohol into Butyl Levulinate
2014
We study the catalytic condensation of furfuryl alcohol with 1-butanol to butyl levulinate. A screening of several commercial and as-synthesized solid acid catalysts shows that propylsulfonic acid-functionalized mesoporous silica outperforms the state-of-the-art phosphotungstate acid catalysts. The catalyst is prepared via template-assisted sol-gel polycondensation of TEOS and MPTMS. It gives 96 % yield (and 100 % selectivity) of butyl levulinate in 4h at 110 °C. Reaction profiles before and after a hot filtration test confirm that the active catalytic species do not leach into the solution. The catalyst synthesis, characterization, and mode of operation are presented and discussed. Sour ca…
Deep oxidation of propane using palladium–titania catalysts modified by niobium
2008
Abstract Pd/TiO 2 catalysts modified by niobium have been prepared and tested for the complete oxidation of propane. The catalysts have been characterised by BET, XRD, laser Raman spectroscopy, XPS, DRS and TPR. The incorporation of niobium into Pd/TiO 2 catalysts resulted in a marked increase in the catalytic activity compared to the Nb-free Pd/TiO 2 catalysts, and the activity increased as the niobium and/or palladium loading increased. The addition of Nb significantly modified the nature of the palladium and niobium species. There was a marked increase in the oxygen mobility after niobium addition. This could not only promote the presence of palladium species in a totally oxidized state …
Fabrication, Electrical Characterization and 1/f Noise Study of Submicron-sized Superconducting Tunnel Junctions
2016
Catalytic Conversion of Glucose and Chlorella sp. into Furans in the Presence of Niobium Oxide
2023
A series of Nb2O5 solid catalysts have been prepared to be used for the catalytic dehydration of glucose and sugars from algae Chlorella sp. into added value furans. The glucose transformation gave rise to 5-hydroxymethylfurfural (5-HMF). Chlorella sp. was used in the same catalytic conditions to be valorised to furans. By preliminary studies we concluded that the algae aqueous suspension needed a previous treatment in the presence of SiO2 pellets to liberate the carbohydrates that in the catalytic reaction in the presence of Nb2O5 materials gave rise 5-HMF and furfural. The best operative conditions and Nb2O5 catalysts were individuated. The most performant Nb2O5 catalyst also showed an ex…
Total absorption γ -ray spectroscopy of niobium isomers
2019
15 pags. 17 figs., 5 tabs.
CCDC 1402554: Experimental Crystal Structure Determination
2015
Related Article: Willian X. C. Oliveira, Cynthia L. M. Pereira, Carlos B. Pinheiro, Joan Cano, Francesc Lloret, Miguel Julve|2015|Chem.Commun.|51|11806|doi:10.1039/C5CC04285B
Applications and non-idealities of submicron Al–AlOx–Nb tunnel junctions
2016
We have developed a technique to fabricate sub-micron, 0.6µm×0.6µm Al-AlOx-Nb tunnel junctions using a standard e-beam resist, angle evaporation and double oxidation of the tunneling barrier, resulting in high quality niobium, as determined by the the high measured values of the critical temperature TC ∼ 7.5 K and the gap ∆ ∼ 1.3 meV. The devices show great promise for local nanoscale thermometry in the temperature range 1 - 7.5 K. Electrical characterization of the junctions was performed at sub-Kelvin temperatures both with and without an external magnetic field, which was used to suppress superconductivity in Al and thus bring the junction into a normal-metal-insulator-superconductor (NI…