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

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