47 research outputs found
Fast determination of phases in LiFePO4 using low losses in electron energy-loss spectroscopy
Experimental valence electron energy loss spectra (VEELS), up to the Li K
edge, obtained on different phases of LixFePO4 are compared to first principles
calculations using the density functional code WIEN2k. In the 4-7 eV range, a
large peak is identified in the FePO4 spectrum, but is absent in LiFePO4, which
could allow the easy formation of energy filtered images. The intensity of this
peak, non sensitive to the precise orientation of the crystal, is large enough
to rapidly determine existing phases in the sample and permit future dynamical
studies. Solid solution and two-phases regions are also differentiated using Fe
M2,3 / Li K edges.Comment: submitted to AP
Multiferroic phase transition near room temperature in BiFeO3 films
In multiferroic BiFeO3 thin films grown on highly mismatched LaAlO3
substrates, we reveal the coexistence of two differently distorted polymorphs
that leads to striking features in the temperature dependence of the structural
and multiferroic properties. Notably, the highly distorted phase
quasi-concomitantly presents an abrupt structural change, transforms from a
hard to a soft ferroelectric and transitions from antiferromagnetic to
paramagnetic at 360+/-20 K. These coupled ferroic transitions just above room
temperature hold promises of giant piezoelectric, magnetoelectric and
piezomagnetic responses, with potential in many applications fields
Electron diffraction (LACBED) and HRTEM Moiré fringe pattern study of stress in YBaCuO thin film on Mg0
Epitaxial stresses are studied by means of Large Angle Convergent Beam Electron Diffraction technique and Moiré fringe pattern obtained by High Resolution Transmission Electron Microscopy in pulsed laser deposited thin films of YBaCuO on MgO substrate. Grains with their c-axis parallel to the interface (c//) grow from the substrate up to the outer surface of the film. The c// grains, embedded in the c ⊥ host matrix, are studied from investigations of cross-sectional sample, by both LACBED performed on the MgO substrate just beneath the different orientations of the thin film, and by the Moiré fringe pattern obtained by tilting the interface of the sample. The broadening of the Bragg lines present in the LACBED disk together with the direction of the Moiré fringes, clearly indicate that the c// oriented grains embedded in a c ⊥ oriented YBaCuO matrix are under stress
Structure and Magnetism of Ni clusters in AlOx: Importance of XAS in the synthesis optimization
Nanostructured sapphire vicinal surfaces as templates for the growth of self-organized oxide nanostructures
International audienceVicinal substrates of sapphire with miscut angle of 108 from the (0 0 1) planes towards the [1 1 0] direction have been annealed in air in the range from 1000 to 1500 8C. The behaviour of these surfaces has been characterized as a function of the temperature and the thermal treatment time by Atomic Force Microscopy observations. A thermal treatment at 1250 8C allows to stabilize a surface made of periodically spaced nanosized step-bunches. Such stepped surfaces were used as template to grow selfpatterned epitaxial oxide nanoparticles by thermal annealing of yttria-stabilized zirconia thin films produced by sol–gel dip-coating. Grazing Incidence Small Angle X-ray Scattering and High-Resolution Transmission Electron Microscopy were used to study the morphology of the nanoparticles and their epitaxial relationships with the substrate
Superconducting properties of lead nanowires arrays
Mesoscopic superconducting lead nanowires with high aspect ratio and diameter ranging from 40 to 270 nm have been grown by electrodeposition inside nanoporous polycarbonate membranes. Nanowires with a diameter less than 50 nm were insulators due to a poor crystal structure. The others are shown to be type II superconductors because of their small electronic mean free path, instead of being type I which is usual for the bulk form of lead. An increase in the thermodynamic critical field H-c is observed and is attributed to the small transversal dimension leading to an incomplete Meissner effect. Finally, it is demonstrated that this enhancement agrees with numerical simulations based on the Ginzburg-Landau theory. (C) 2002 Elsevier Science B.V. All rights reserved