Single-phase spinel manganese cobalt oxides Mn 3Àx Co x O 4 dense ceramics were prepared for the first time and their structural/electrical property relationships characterized. The electrical properties, that is, the resistivity at 25°C, the energetic constant, and the resistance drift at 125°C, were determined and correlated with the cation distribution. Finally, the electrical characteristics of the Mn 3Àx Co x O 4 system were compare'd with other important classes of manganese-based spinel oxides, Mn 3Àx Ni x O 4 and Mn 3Àx Cu x O 4 , already commercialized as negative temperature coefficient (NTC) thermistors. The high values of energetic constant and low resistivities observed in Mn 3Àx Co x O 4 ceramics present a promising interest for such industrial applications. *tenailleau@chimie.ups-tlse.fr
Coherent 3D parts of cermets, made of spinel ferrite and metallic copper, are prepared in a nitrogen atmosphere by powder bed additive manufacturing of a mixture of oxide and metallic powders. The cermets obtained are constituted by the association of blocks of about 500 µm, which create between them, a relatively large porosity (# 35%). Each block is subdivided into inti mately nested wnes that are either predominantly metallic or pre dominantly oxide type. ln the metal parts, a dispersion of oxide crystals is observed, whose siz.e varies from ten nanometers to a few micrometers. A similar distribution of metal particles in the oxide zones is also demon strated. The chemical compositions of metallic and oxide phases are slightly different from those in the initial powders. Due to the high energy density of the laser, the melting temperature of the metal and oxides could be reached and therefore this could explain the chemical composition variations in the phases and the shape of oxide and metallic nanometric grains. The process used can therefore be described as powder bed fusion. These nanostructured cermets have been used as 'înert" anodes for the electrolysis of aluminum in molten cryolite. Although penalized by a high porosity, 5 mm in diameter anodes allowed to carry out an electrolysis for 4 h. Sinoe Spark Plasma Sintering can greatly reduoe their porosity, while retaining their specifi c microstructure, the implementation of additive manufacturing for producing "inert" anodes is therefore of real interest
Nanocrystalline CuO-CuxFe3-xO4 thin films were developed using a radio-frequency sputtering method followed by a thermal oxidation process. Thin films were deposited applying two very different conditions by varying the argon pressure and the target-tosubstrate distance. Structural, microstructural and gas-sensing characteristics were performed using grazing incidence X-ray diffraction (GXRD), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electrical measurements. Their sensing properties were examined using hydrogen gas in dry synthetic air. The shortest response and recovery times were observed between 280 and 300 °C independently of the deposition conditions.
ZnO nanostructured materials in thin film forms are of particular interest for photovoltaic or photocatalysis processes but they suffer from a lack of simple methods for optimizing their microstructure. We have demonstrated that microporous ZnO thin films with optimized inter grain accessibility can be produce by radio frequency magnetron sputtering process and chemical etching with 2.75 mM HCl solution for different duration. The as-deposited ZnO thin films were first characterized in terms of structure, grain size, inter grain space, open cavity depth and total thickness of the film by XRD, AFM, SEM, profilometry and optical measurements. A specific attention was dedicated to the determination of the surface enhancement factor (SEF) by using basic geometrical considerations and images treatments. In addition, the porous fraction and its distribution in the thickness have been estimated thanks to the optical simulation of the experimental UV-Visible-IR spectrums using the Bruggeman dielectric model and cross section SEM images analysis respectively. This study showed that the microstructure of the as-deposited films consists of a dense layer covered by a porous upper layer developing a SEF of 12-13 m 2 m −2. This two layers architecture is not modified by the etching process. The etching process only affects the upper porous layer in which the overall porosity and the inter-grain space increase with the etching duration. Column diameter and total film thickness decrease at the same time when the films are soaked in the HCl bath. The microporous structure obtained after the etching process could generate a great interest for the interfaces electronic exchanges for solar cells, photocatalysis and gas sensors applications.
Thin films of defect spinel ferrites can be used as write-once read-many
media working with blue wavelengths. In fact, because these non-stoichiometric
ferrites are metastable, they can be transformed into corundum phases at moderate
temperatures by a laser spot. The transformed regions have different optical
indices from the starting ferrite film, making the readout process possible.
Recording density of about 5 bits/µm2 was demonstrated.
International audienceIron cobaltite thin films with spinel structure have been elaborated by radio-frequency (RF) magnetronsputtering from a Co1.75Fe1.25O4 target. Influence of argon pressure on structure, microstructure and physicalproperties of films has been examined. Iron–cobalt oxide thin films essentially consist of one spinel phasewhen deposited at low pressure (0.5 and 1.0 Pa). At high pressure (2.0 Pa), the global stoichiometry of the filmis changed which results in the precipitation of a mixed monoxide of cobalt and iron beside the spinel phase.This in-situ reduction due to an oxygen loss occurring mainly at high deposition pressure has been revealed byX-ray diffraction and Raman spectroscopy. Microstructural evolution of thin film with argon pressure has beenshown by microscopic observations (AFM and SEM). The evolution of magnetic and electrical properties, versusargon pressure, has been also studied by SQUID and 4 point probe measurements
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