Controlled synthesis of CoFe2O4 nano-octahedra

International audienceNano-octahedral grains of cobalt ferrite (CoFe2O4) with size around 20 nm were synthesized by a hydrothermal route. X-rays and electron diffraction, along with scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and thermogravimetric analysis were used to characterize the powders. Images and simulations of high-resolution electron microscopy allowed the identification of the shape of the grains. Process parameters such as temperature and time of reaction, reagents concentration, and pH of the reacting medium were optimized. The surfactant cetyltrimethylammonium bromide (CTAB) hindered the formation of goethite, which favored the production of a pure CoFe2O4 powder. The oxidation state of cobalt atoms on the ferrite structure was also influenced by CTAB. The control of the shape of the grains was associated mainly to the nature of the precipitating agent

Magnetic, electric and thermal properties of cobalt ferrite nanoparticles

International audienceThe electric and magnetic properties as well as the thermal stability of CoxFe3-xO4 nanopowders, (0.

Crystal growth and characterization of the ruthenate superconducting compound: Sr2RuO4

International audienceSr2RuO4 is a copper-free layered perovskite superconductor with the tetragonal K2NiF4-type structure. The precise nature of the pairing in the superconducting state of this material is still under debate. In this paper, we report about crystal growth and characterization of this compound. The crystals were grown by a floating zone technique using a light furnace equipped with double elliptical mirrors starting from off-stoichiometric Sr2RuO4. The crystals have been checked by X-ray diffraction and microanalysis. The superconducting properties were measured by AC-susceptibility, magnetization and specific heat. High crystalline quality centimetre-sized crystals have been grown and best crystals exhibit superconducting transitions at View the MathML source (typical dimensions : 4.5 mm diameter and 70 mm length with the (0 0 1) axis perpendicular to growth direction). The unconventional superconductors are characterized by a drastic impurity effect on the superconducting properties. We try to establish a correlation between the defect concentration and the physical properties of Sr2RuO4

Synthesis and microstructure of cobalt ferrite nanoparticles

International audienceCobalt ferrites (CoxFe3-xO4) nanoparticles with various compositions were synthesized by a new non-aqueous synthesis method. The cobalt ferrites were characterized by X-rays diffraction, and transmission electron microscopy coupled with energy dispersive spectroscopy. The nanoparticles are highly crystallized, with a homogeneous chemical composition. The particle size varies from 4 nm up to 7.5 nm, depending on the cobalt content. The smallest particles, with a size of 4 nm, are obtained for high cobalt content. These particles have also the highest micro-structural strain. Catalytic measurements were realized using Fourier Transform Infrared Spectroscopy. The lowest activation energy and the highest conversion rate are obtained for Co1.8Fe2.4O4, in the 400-500°C temperature range

Sr4Ru2O9 films grown by pulsed laser deposition

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A facile one step route to synthesize WO 3 nanoplatelets for CO oxidation and photodegradation of RhB: microstructural, optical and electrical studies

International audienceTwo-dimensional nanoplatelets of tungsten trioxide (NP-WO3) were synthesized at room temperature, using a wet chemical method, without any surfactants or templates; aqueous mineralization was obtained by simply adjusting the pH. The resulting nanostructures were characterized using X-ray diffraction combined with Rietveld refinements, Raman and UV-Vis spectroscopies. Their morphologies and sizes were analyzed by scanning and electron microscopies. The electrical, optical, catalytic and photocatalytic properties of the NP-WO3 nanoplatelets were then determined and compared to the ones of pseudospherical (PS-WO3) standard samples. Nanoplatelets as well as pseudospherical particles crystallized in the single orthorhombic WO3 phase. The Rietveld refinement calculations and HRTEM analyses revealed a strong distortion of the WO6 octahedra, according to the W-O splitting. The electrical conductivity of WO3 compact pellets showed that both samples were semi-conducting with a weak difference in activation energies. Using a homemade photocatalytic device, the NP-WO3 particles used as photocatalyst in an aqueous medium, exhibited a significant efficiency to decompose rhodamine B over their large exposed surface (010), compared to PS-WO3 particles. These NP-WO3 particles were also used as the catalytic material for oxidation in an air-CO gas flow. They exhibited catalytic activity higher than the one in the PS form

Possible room-temperature ferromagnetism in K-doped SnO2: X-ray diffraction and high-resolution transmission electron microscopy study

International audienceAb initio studies have theoretically predicted room-temperature ferromagnetism in crystalline SnO2, ZrO2, and TiO2 doped with nonmagnetic element from the 1A column as K and Na. Our purpose is to address experimentally the possibility of magnetism in both Sn1−xKxO2 and Sn1−xCaxO2 compounds. The samples have been prepared using equilibrium methods of standard solid-state route. Our study has shown that both Sn1−xCaxO2 and Sn1−xKxO2 structure is thermodynamically unstable and leads to a phase separation, as shown by x-ray diffraction and detailed microstructural analyses with high-resolution transmission electron microscopy. In particular, the crystalline SnO2 grains are surrounded by K-based phase. In contrast to Ca:SnO2 samples, we have obtained a magnetic phase in K:SnO2 ones but no long-range ferromagnetic order. The K:SnO2 samples exhibit a moment on the order of 0.2 μB/K /ion, in contrast to ab initio calculations which predict 3 μB, where K atoms are on the Sn crystallographic site. The apparent contradictions between our experiments and first-principles studies are discussed

Ferroelectric Bi3.25La0.75Ti3O12 thin films on a conductive Sr4Ru2O9 electrode obtained by pulsed laser deposition

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Effect of WO3 Nanoparticles Morphology on the Catalytic Properties

1st International Conference on Advances in Functional Materials (AFM), Stony Brook Univ, Stony Brook, NY, JUN 29-JUL 03, 2015International audienceTungsten trioxide WO3 powder have been synthesized at room temperature with aqueous mineralization processes, with two distinct morphologies: nanoplates and pseudospheres. The aim of this work is tohighlight the influence of the nanoparticles morphology on the carbon monoxide CO catalytic gaseous transformation and photocatalytic decomposition of Rhodamine in aqueous medium. The samples were characterized by X-ray diffraction, scanning and transmission electron. The nanoplates of WO3 show significantly higher photocatalytic activity than the pseudospheres, due to the large surface area. The CO oxidation was performed under air and the conversion reaction is not complete leaving residual CO and without shape effect. (C) 2016 Elsevier Ltd. All rights reserved

Morphology and composition tailoring of CoxFe3 − xO4 nanoparticles

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