Ferroelectric BaTiO3 single crystal under superstrong electric fields up to 55 MV/m: A comparative experimental and theoretical study

International audienceWe investigated the effect of huge electric field up to E=55 MV/m on tetragonal ferroelectric phase of BaTiO3 single crystal. Both lattice parameters and the dielectric susceptibility along the polar axis were determined. The induced polarization shows a continuous increase up to 20% of the spontaneous polarization. The longitudinal d(33) and transverse d(31) piezoelectric coefficients were also determined. The experimental data are described by a phenomenological approach. Interestingly, an intermediate critical electric field value of E similar to 25 MV/m was evidenced suggesting that the physics below and above this value are differen

New life of a forgotten method: Electrochemical route toward highly efficient Pt/C catalysts for low-temperature fuel cells

International audienceDriven by global environmental concerns, great efforts are currently made to develop novel, cheap and practical means for producing highly efficient electrocatalysts, specifically for the low-temperature fuelcell applications. Employing an old but yet unexplored method based on electrochemical dispergation of platinum by the alternating current, we show that the freshly prepared Pt/C catalysts exhibit greatly enhanced catalytic activity (up to 350% for oxygen reduction and up to 200% for ethylene glycol oxidation) as compared with that of a commercially available counterpart (E-TEK). A key role in these reactions is attributed to a specific nanoparticle morphology. These findings should provide a revival of an ancient but simple and efficient electrochemical process and motivate further researches in the field

XRD and electrochemical investigation of particle size effects in platinum-cobalt cathode electrocatalysts for oxygen reduction

International audiencePt-Co/C electrocatalysts with Pt loadings near 30 wt. % prepared by the impregnation method in water - ethylene glycol solutions were investigated by X-ray diffraction and correlated with electrochemical measurements. We show that the composition of the binary solvent controls the average particle size and its distribution. The unit cell parameter of the Pt3Co alloy decreases nonlinearly with decreasing particle size. The ORR activity of the prepared Pt-Co/C catalysts in H2SO4 solution enhances with decreasing particle size and unit cell parameter as well as with narrowing of the particle size distribution. Corrosion treatment of the synthesized Pt-Co/C materials causes an increase of ca. 1 nm in average particles size accompanied by broadening of the particle size distribution and decreasing Co content in the Pt-Co alloy. All of the synthesized Pt-Co/C materials show higher ORR activities than do the commercial Pt/C electrocatalysts

Catalytic activity of carbon supported Pt nano(electrocatalysts. Why reducing the size of Pt nanoparticles is not always beneficial

International audienceCarbon-supported Pt catalysts prepared by the impregnation method in water - dimethyl sulfoxide (DMSO) solutions were investigated. Using X-ray diffraction (XRD) technique for estimation of the particle size and shapes, we show that morphology of the Pt/C catalysts depends strongly on the DMSO content in the solutions. The average particles size reduces and a shape of the Pt nanocrystals changes from a truncated octahedron to a cuboctahedron, and eventually to a truncated cube with increasing DMSO concentration in the reaction mixture. Antibate effects of the size and shape cause non-monotonic dependence of the catalytic activity for the oxygen reduction reaction (ORR) with electric current maximum at an average particle size of 2.7nm

Characterization of an UO2 ceramic via Raman imaging and electron back-scattering diffraction

International audienc

Thin ferroelectric Nd-doped BiFeO3 films with orthorhombic structure

International audienceX-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on MgO substrates reveal their orthorhombic symmetry Fmm2 (a = 7.914 Å, b = 7.913 Å, and c = 7.937 Å). © 2010 Allerton Press, Inc