2,089 publications from this institution
Superconductivity is found in tetragonal La3−x Ba3+x Cu6O14+δ and La, Ba)6−x Sr x Cu6O14+δ even though they do not possess Cu-O chains or the K2NiF4 structure. Resistivity measurements confirm the occurrence of a transformation from chain-superconductivity to sheet-superconductivity in YBa2Cu3O7−δ as δ is varied in the range 0.0–0.5. \n
A generalized formulation is described of the evaluation of configurational energies of isolated defects and defect pairs which includes an improved treatment of the relaxation of ions nearest to the defects. The energies of association between vacancy pairs and divalent cation impurity-vacancy pairs in the first three associated states of KCl are calculated employing this method and these values are compared with earlier theoretical estimates.
Infrared spectra of La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7-δ are discussed, specially with respect to the disappearance of the high-frequency (~650 cm) band of the superconducting compositions at 300K. Some of the bands persist at 300K eventhough the materials are fairly conducting. YBa 2 Cu 3 O 7-δ does not show evidence in the far IR spectrum for the presence of an optical gap.
We report a facile method to generate MoS2/single-walled carbon nanotubes (SWCNT) and MoS2/borocarbonitride (BC6N) composites by mixing MoS2 nanoparticle dispersion with different proportions of carboxyl-functionalized SWCNT and BCN in water. The MoS2/SWCNT and MoS2/BCN composites show higher electrocatalytic H2 evolution performance compared to the individual constituents, the activity increasing with the proportion of MoS2. Among the prepared catalysts, MoS2-SWCNT with a 3:1 ratio of MoS2 and SWCNT exhibits highly positive onset potential (-113 mV vs RHE) and a small Tafel slope (59 mV dec−1) as well as remarkable stability in acid electrolyte. The combination of MoS2 nanoparticles with SWCNT or BCN appears to be a valuable finding with applications in catalysis reactions.
ReO3 nanoparticles in the diameter range of 8.5-32.5 nm have been prepared by decomposition of the Re2O7-dioxane complex under solvothermal conditions and characterized by X-ray diffraction, electron microscopy, optical spectroscopy, and scanning probe microscopy. The nanoparticles have the cubic (Pm3m {221} space group) structure with the lattice parameter increasing with decreasing size. The particles are metallic and show a plasmon band around 520 nm, which becomes blue-shifted with a decrease in size. The metallicity of the nanoparticles is also confirmed by tunneling conductance measurements. The nanoparticles show paramagnetic or diamagnetic behavior depending on the size, with evidence for superparamagnetism at low temperatures when the size is small.
No abstract is provided for this article.
Indium-doped GaN nanocrystals with 5% and 10% In have been prepared by a low temperature solvothermal method using hexamethyldisilazane as the nitriding reagent. The nanocrystals show Raman bands at lower frequencies compared to GaN. Photoluminescence spectra of the In-doped GaN nanocrystals exhibit an increase in the FWHM with the decrease in the PL band energy, the band energy itself decreasing with increase in the In content.
Interesting correlations between the superconducting transition temperatures of cuprates and various structural and electronic parameters are discussed. 123–124 transformation in oxygen-deficient 123 cuprates and some features of the oxyanion cuprate derivatives are examined.
The effects of the interactions of metal ions with lipoic acid-capped Ag and Au nanoparticles have been studied by the combined use of electronic absorption spectroscopy and transmission electron microscopy. Three types of effects that are dependent on the metal ion concentration can be distinguished. First, in the dilute regime, there is reversible chelation of the metal ions, causing a marked dampening of the plasmon resonance band of the nanoparticles, but there is no aggregation. The magnitude of plasmon dampening depends on the nature as well as the concentration of the metal ions. In the intermediate concentration regime, aggregation occurs, but in the high concentration regime, there is precipitation. These different regimes are clearly evidenced in the changes in the electronic spectra and in the electron micrographs.
The metathesis reaction between CdCl 2 ·2H 2 O and sodium oxalate in n ‐hexanol under solvothermal conditions yields a hybrid compound of formula Cd 2 (C 2 O 4 ) 0.5 Cl 3 NaCl·4H 2 O. It consists of one‐dimensional chains formed by Cd and Cl atoms, containing μ 2 (Cl) and μ 3 (Cl) bridges, and cross‐linked by oxalate units to give a layered structure. The Na + ions and water molecules occupy the interlamellar spaces. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The superconducting Tc in the various copper oxides shows a broad maximum at a certain value of the nominal Cu3+ Cu2+ ratio. The significance of this important feature is discussed and a model based on strong correlations is suggested to explain the results.
A novel example of a photo-induced single-crystal to single-crystal phase transformation is described for title compound; the accompanying change in molecular conformation is rationalised in terms of an intermediate excimeric state.
Following the discovery of carbon fullerenes and carbon nanotubes, it was hypothesized that nanoparticles of inorganic compounds with layered (two–dimensional) structure, such as MoS2, will not be stable against folding and form nanotubes and fullerene–like structures: IF. The synthesis of numerous other inorganic nanotubes has been reported in recent years. Various techniques for the synthesis of inorganic nanotubes, including high–temperature reactions and strategies based on ‘chemie douce’ (soft chemistry, i.e. low–temperature) processes, are described. First–principle, density functional theory based calculations are able to provide substantial information on the structure and properties of such nanotubes. Various properties of inorganic nanotubes, including mechanical, electronic and optical properties, are described in brief. Some potential applications of the nanotubes in tribology, protection against impact, (photo)catalysis, batteries, etc., are discussed.
Lifetimes of positrons annihilating in NH4Cl and in nitrate glasses have been measured as a function of temperature. The observed temperature dependence of tau 2 and I2 indicates that the I2 is significantly affected by changes in molar volumes accompanying the phase transitions in these solids. I2 varies in the same direction as the molar volume thus underlining the role of free volume in the positron annihilation process in condensed media.
