A new L-PBF process is proposed to manufacture, from a single powder chemically activated by pure hot water, parts comprising in selected areas of space, a ceramic or a metal alloy. The chemical activation of the starting alloy powder, the melting and densification of the metallic zones as well as the oxidation of metal alloy powder and sintering of the ceramic zones, have been studied and optimized. The results obtained allowed the realization of multi-material functional structures. Thus, small coaxial conductors have been fabricated. Beyond these relatively simple parts, 2D and 3D periodic structures made of ceramics and metal have been successfully realized. The achievement of these periodic structures gives hope for the further development of 3D inorganic metamaterials for microwave applications.

Fe–Ni alloy based powders of different stoichiometry and purity were synthesized by thermal decomposition of a co-precipitated oxalic precursor. By modifying the oxygen partial pressure of the gaseous flow, a nearly pure Fe64Ni36 Invar powder and a composite Fe50Ni50-Fe3O4 powder were prepared. The composite particles present an original microstructure consisting of an intimate mixture of Fe50Ni50 and Fe3O4 submicronic grains. The behavior of the composite powder was studied in laser powder bed fusion (LPBF) process. Reduction of iron oxide and specific microstructural changes were revealed. Subsequent conventional heat post-treatment allowed to remove the remaining iron oxides and to form porous multiphase Fe–Ni alloy 3D parts. Repeatable heterogeneities of microstructure and composition, at a periodicity corresponding to the thickness of the powder bed used in the LPBF process, constitute the hallmark of the laser treatment carried out on the composite powder.

Films deposited on glass substrate by RF sputtering, were heat treated in air by a low power laser spot thanks to conventional photolithography machine, to obtain pure CuCr0.97Mg0.03O2 delafossite with an optical transmittance of 0.58 and a conductivity of 5.8S.cm(-1). The Haacke's figure of merit is improved to reach 2.07 x 10(7)Omega(-1). Laser annealing by a photolithography machine is thus very interesting for enhancing the p-type transparent conductor properties of such delafossite phases. A local annealing according to selected patterns could also be envisaged, opening up exciting prospects for fast and low cost making the most of these transparent ptype semiconductors.

Rings based on pure iron have been manufactured by laser powder bed fusion. Different experimental conditions have been implemented to manufacture simple rings called "bulk". Selected conditions were used to fabricate "structured" rings, made up of stacking of lamellae separated by weakly densified metal zones or by spacers. The magnetic properties of these rings were measured in order to determine their maximum flux density, their permeability and their magnetic losses. These properties, as well as the organizations of the magnetic domains observed by Magnetic Force Microscopy, were compared with those obtained for rings machined from castings parts or spark plasma sintered parts. The "bulk" rings resulting from laser fusion exhibit relatively high magnetic losses of the order of 80 W.kg−1 at 50 Hz under 1 T. However, this value can be lowered to about 30 W.kg−1 after a SPS treatment at 750 °C. In addition to lowering the magnetic losses, SPS annealing increases the densification of the material and thus the magnetic flux. The spacing of dense metal rings by less sintered zones or by spacers ("structured rings"), makes it possible to also greatly reduce the magnetic losses. Dividing these losses by a factor of 2 is thus possible by implementing a simple geometric arrangement.

A new process using the selective decomposition of silver oxalate is presented and applied to the production of transparent electrodes on a polymer substrate. It is indeed shown that the silver oxalate Ag 2 C 2 O 4 can be reduced to the metallic silver state by the focused laser beam of a photolithography machine (λ = 405 nm, spot size 5 µm, power between 3 and 100 mW). Thin lines of silver of width close to 15 µm, for optimized insolation conditions, can thus be directly and easily, formed in a layer of oxalate deposited by spin coating on polycarbonate substrate. Since the metal and the oxalate are of very different chemical natures, the residual oxalate is dissolved by an ammoniacal solution without affecting the metal. The silver conductive lines have a very porous vermicular type microstructure which, however, ensures electrical conductivity. The resistive effects, which result from this not very compact filament organization, can be reduced by simply applying a uniaxial mechanical pressure perpendicular to the plane of the substrate. This operation irreversibly reduces the porosity by crushing the silver strands. One by one-centimeters samples with an electrical resistance of 10 Ω and an optical transparency of 95% (after correcting the effects of the substrate) were thus prepared. Their factor of merit expressed by (Transparency 550nm ) 10 / R pattern , close to 0.059 Ω −1 , is at the state of the art. The selective decomposition of silver oxalates by a laser beam is therefore a very interesting way to easily make transparent conductors made of thin metallic patterns.

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 mu m, which create between them, a relatively large porosity (# 35%). Each block is subdivided into intimately nested zones that are either predominantly metallic or predominantly oxide type. In the metal parts, a dispersion of oxide crystals is observed, whose size varies from ten nanometers to a few micrometers. A similar distribution of metal particles in the oxide zones is also demonstrated. 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 "inert" 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. Since Spark Plasma Sintering can greatly reduce their porosity, while retaining their specific microstructure, the implementation of additive manufacturing for producing "inert" anodes is therefore of real interest.

Tests on NixFe3-xO4 spinels, considered as promising materials in the aluminium production, were performed on Fe3O4 and NiFe2O4. First, FeAl2O4 aluminate was spontaneously formed by Fe3O4 immersion at 960 degrees C, due to Fe3+/Al3+ substitution into the spinel structure. Then, stability of aluminate compound was investigated into cryolite melt and results showed a rapid dissolution when the aluminate composition tends to FeAl2O4. Kinetic studies demonstrated that the spinel dissolution was around twentyfold higher than aluminate formation, confirming the micrographic observation. To prevent it, nickel was added in the spinel structure up to NiFe2O4 and no dissolution was observed.

The synthesis and characterization of magnesium ferrite MgFe2O4 prepared by co-precipitation and sol gel combustion is reported. Structural characterization showed that all the samples have single spine! phase. The co precipitated sample exhibits smaller grains and twice higher BET surface than the sol gel combustion samples. The powder was shaped to dedicated chemo-resistive home-made sensors devices. The electrical properties and sensing properties towards carbon dioxide of both MgFe2O4 powders were studied. The type of cWar& crrieff were analysed on the basis of the change in resistance in the presence of air and argon. The sensing response towards CO2 was found to be dependent on the morphology of the powder sample and the CO2 concentration. A high response of 36% towards 5000 ppm of CO2 was reached which is good for this gas. The key role of the Mg ions modulating the electrical properties is discussed.

Films of copper and cobalt-iron oxalates were prepared from suspensions of powders in ethane-1,2-diol deposited on glass or polycarbonate substrates. Two-dimensional structures of oxides, resolved on the scale of less than ten micrometers, were formed by laser insolation of these films, using a photolithography machine. The nature of the constitutive phases of the oxides formed tends to show that the laser heating makes it possible to reach locally, temperatures higher than 1000°C. The oxides formed are thus sintered. The residual oxalate can be removed by washing or dissolving, leaving the oxide structure on its substrate. In spite of a perfectible sintering, the formed structures could interest different technological applications (electronic or magnetic devices, gas sensors, photovoltaic systems…) requiring the shaping of simple or mixed oxides on a scale close to the micrometer. The process of selective laser decomposition of oxalates, could subsequently be suitable for additive manufacturing of 3D parts.

The paper reports the synthesis and characterization of cuprite/copper ferrite nanopowder composites. The composites were synthesized using co-precipitation with oxalates precursor route. The phase and microstructure of the powder samples were characterized using X-ray diffraction, BET surface area analyzer and scanning electron microscopy. The powders were fabricated to device using a simple and efficient shaping technique. These devices were used further to carry out electrical property measurements in various atmospheres. The type of charge carriers were found by noting the sense of change in resistance when the air atmosphere on the sample was replaced with argon. CO2 responses were reported for the whole series of composites. The effect of cuprite concentration on the CO2 sensing performance was found to be independent of cuprite concentration up to certain limits (70%at).

Iron cobaltite thin films with spinel structure have been elaborated by radio-frequency (RF) magnetron sputtering from a Co1.75Fe1.25O4 target. Influence of argon pressure on structure, microstructure and physical properties of films has been examined. Iron–cobalt oxide thin films essentially consist of one spinel phase when deposited at low pressure (0.5 and 1.0Pa). At high pressure (2.0Pa), the global stoichiometry of the film is 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 by X-ray diffraction and Raman spectroscopy. Microstructural evolution of thin film with argon pressure has been shown by microscopic observations (AFM and SEM). The evolution of magnetic and electrical properties, versus argon pressure, has been also studied by SQUID and 4 point probe measurements.

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. (C) 2015 Elsevier B.V. All rights reserved.

Some spinel ferrites can be oxidized or transformed at moderate temperatures. Such modifications were carried out on thin films of mixed cobalt copper ferrites and maghemite, by heating small regions with a low-power laser spot applied for about 100 ns. The very simple laser heating process, which can be done directly with a conventional photolithographic machine, made it possible to generate two-dimensional magnetization heterogeneities in ferrimagnetic films. Such periodic structures could display the specific properties of magneto-photonic or magnonic crystals. (c) 2013 Elsevier B.V. All rights reserved.

Single‐phase spinel manganese cobalt oxides Mn3−xCoxO4 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 Mn3−xCoxO4 system were compare'd with other important classes of manganese‐based spinel oxides, Mn3−xNixO4 and Mn3−xCuxO4, already commercialized as negative temperature coefficient (NTC) thermistors. The high values of energetic constant and low resistivities observed in Mn3−xCoxO4 ceramics present a promising interest for such industrial applications.

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-to-substrate 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 degrees C independently of the deposition conditions. (C) 2010 Elsevier B.V. All rights reserved.

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-to-substrate 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.

Ga-doped ZnO (ZnO:Ga) thin films were prepared by radio-frequency–magnetron sputtering on conventional glass substrates at room temperature. The structural, electrical, and optical properties of these films as a function of argon pressure and film thicknesses were studied. All the films crystallized with the hexagonal wurtzite structure. The x-ray diffraction studies show that the ZnO:Ga films are highly oriented with their crystallographic c-axis perpendicular to the substrate. We discuss a methodology of using a “standardized platform” for comparison of samples deposited at different pressures, which provides an insight into the defect–resistivity relationship of each sample with respect to their microstructure. After the first annealing, the electrical properties of the films are dependent on the atmosphere used during postdeposition annealing treatment. A resistivity of 2.5 × 10-3 Ω-3· cm was obtained after vacuum annealing, and the films became an insulator after air annealing. The reproducibility of this treatment was verified. The average transmittance of all ZnO:Ga thin films is more than 85% in the visible range.

Dense micro-cermets made of nickel ferrites and copper micrometric particles were obtained from partial reduction under hydrogenated atmosphere at 350 degrees C of mixed copper nickel ferrites, and sintering in nitrogen at 980 degrees C. The small copper particles are homogeneous in size and well dispersed in the spinet oxide matrix No exudation of copper metal was observed after sintering. The micro-cermets prepared are semi-conducting materials with electrical conductivity lying from 44 to 130 S/cm at 980 degrees C. Their overall characteristics make them interesting for inert anodes dedicated to aluminium electrolysis in melted cryolite. (C) 2009 Elsevier Masson SAS. All rights reserved.