Evaluation of a sol–gel process for the synthesis of La1−xSrxMnO3+δ cathodic multilayers for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are electrical energy conversion devices with high efficiency and low pollution. In order to increase performances of SOFCs at intermediate temperature (700–800 °C) and to decrease materials cost, an alternative sol–gel synthesis method has been investigated to deposit La1−xSrxMnO3+δ (LSMx) as cathode thin films. Polycrystalline LSMx thin films were prepared by dip-coating using a polymeric solution. Lanthanum, strontium and manganese nitrates were used as raw materials. The viscosity of the solution was adjusted and the solution was deposited on polycrystalline ZrO2–8% Y2O3 ceramics. Prior to experiments, the substrate surface was eroded until a roughness of 20 nm and then cleaned with ethanol and dried. Film thicknesses were adjusted with the number of layers. Porosity and grain size of monolayers or multilayers were evaluated. Typical thickness of monolayer is 250 nm. A key parameter in the multilayer process was the intermediate calcination temperature (400, 700 or 1000 °C) of each further layer deposition. A correlation between this intermediate temperature and morphology, thickness and porosity was found; porosity is ranging from 3 to 40% and thickness can reach 1 micron for multilayers. Concerning electrochemical performances, the best results were obtained for LSM0.4 multilayers with an intermediate calcination temperature (called Ti) of 400 °C

Out-of-centre distortions around an octahedrally coordinated Ti4+ in BaTiO3

The prototypical ferroelectric system BaTiO3 is an oxide with a perovskite-type structure that exhibits a textbook example of multiple phase transitions associated with an out-of-centre distortion of the octahedral Ti4+ cations. This research combines the double-well potentials model and the bond valence model, to provide an explanation for the cubic–tetragonal–orthorhombic–rhombohedric phase transition sequence. It is shown that to consider the atomic displacements can only occur in the strict respect of their valence, which is calculated with the bond valence model, is sufficient to lead to the clear prediction of the whole transition sequence

New examination of the magnetic properties of cobalt-doped ZnO diluted magnetic semiconductors

Polycrystalline Zn1−xCoxO diluted magnetic semiconductors were prepared within a large doping concentration range from 0.5% to 10%. Thanks to a model based on the co-existence of two magnetic populations, our analysis of the magnetization measurements brings new evidence about the competition between ferromagnetic and antiferromagnetic mean field within the ZnO diamagnetic matrix. It is a temperature activated phenomenon that supports the alignment of individual Co2+ ions into superparamagnetic clusters. At the same time, the refined effective number of antiferromagnetically coupled Co2+ ions is equal to the probability of Co2+ ions belonging to a dimer

(Ca²⁺, V⁵⁺) co-doped Y₂Ti₂O₇ yellow pigment

(Ca2+, V5+) co-doped Y2Ti2O7 yellow pigments were prepared by solid route. The influence of the annealing temperature, the vanadium rate (0.02 ≤ x ≤ 0.3) and a post-mechanical grinding on the phase purity and the colour were studied using X-ray diffraction and UV-vis spectroscopy. The correlation between pigment colouration, synthesis parameters and structural feature is then discussed. Pigments with various colourations from yellow to deep orange can be obtained depending on the synthesis parameters linked to a slight modification of the vanadium coordination environment. For a same composition, the pigment colouration depends on the creation of Frenkel pairs inside the structure corresponding to a displacement of an oxygen atom toward one interstitial empty site

ZnAl2O4 as potential sensor : variation of luminescence with thermal history

ZnAl2O4 spinel powders were prepared using the Pechini or co-precipitation synthetic route and were then treated at different temperatures (600-1350 °C). These powders were characterised by X-ray diffraction, scanning electron microscopy (SEM), diffuse reflectance and luminescence measurements. SEM investigations and the X-ray patterns showed that the spinel crystallite size was dependent on the synthetic route and the treatment temperature. In addition, the structural evolution was investigated by Rietveld refinements. The inversion rate decrease was correlated with the temperature, leading to a direct spinel phase for the sample treated at high temperature. Furthermore, luminescence measurements showed various emissions linked to the presence of defects in the matrix structure. The two main emissions observed were attributed to oxygen vacancy and Zn in the interstitial positions (as revealed by differential Fourier maps). The luminescence spectra exhibited strong differences between 1200 °C and 1350 °C. At the higher temperature, the characteristic emission spectra can be attributed to the direct spinel phase. The indirect-direct spinel transformation can be monitored through the change in the optical properties and correlated to the thermal history of the sample

From nano-structured polycrystalline spheres with Zn1-xCoxO composition to core-shell Zn1-xCoxO@SiO2 as green pigments

ZnO doped with Co2+, a well-known green pigment which is an alternative to the chromium based inorganic pigments, has been prepared by a polyol process and investigated in terms of crystallographic structure and UV–visible properties. Thanks to the obtaining of nanometric crystallite size from our process, the incorporation of a very high concentration of Co2+ in the ZnO matrix is achieved. Thus, different grades of more or less deep green pigments can be produced. Furthermore, the obtaining of spherical aggregates allows the easy preparation of ZnO:Co@SiO2 core-shells, minimizing hence the problems linked to the zinc oxide high solubility into slightly acidic conditions acidic conditions and the metal cation's toxicity.Revêtements Piézochromes Réversibles pour la Détection d'Impacts sur Supports Composite

Mo addition for improved electrochromic properties of V2O5 thick films

International audienceTransition metal oxides (TMOs) have attracted considerable attention due to their variety of chromogenic properties. Among them, vanadium pentoxide (V2O5) has gained significant interest in respect of multichromism associated with orange, green and blue colors. Herein, we report a simple and easy method for the fabrication of Mo doped V2O5 thick films, leading to improved cyclability. Molybdenum doped vanadium pentoxide powders were synthesized from one single polyol route through the precipitation of an intermediate precursor: molybdenum doped vanadium ethyleneglycolate (Mo doped VEG). The as-synthesized Mo-doped V2O5 exhibits improved electrochromic performance in terms of capacity, cycling stability, and color contrast compared to single-component V2O5 in lithium as well as sodium based electrolyte. The improvement in EC performances lies in films of higher porosity as well as higher diffusion coefficients. To conclude, an electrochromic device combining Mo-V2O5 to WO3.2H2O, via a PMMA-lithium based electrolyte membrane exhibits simultaneously reversible color change from yellow to green for Mo-V2O5 and from blue to yellow white for WO3.2H2O with a cycling stability up to 10 000 cycles

Low-Cost and Facile Synthesis of the Vanadium Oxides V2O3, VO2, and V2O5 and Their Magnetic, Thermochromic and Electrochromic Properties.

In this study, vanadium sesquioxide (V2O3), dioxide (VO2), and pentoxide (V2O5) were all synthesized from a single polyol route through the precipitation of an intermediate precursor: vanadium ethylene glycolate (VEG). Various annealing treatments of the VEG precursor, under controlled atmosphere and temperature, led to the successful synthesis of the three pure oxides, with sub-micrometer crystallite size. To the best of our knowledge, the synthesis of the three oxides V2O5, VO2, and V2O3 from a single polyol batch has never been reported in the literature. In a second part of the study, the potentialities brought about by the successful preparation of sub-micrometer V2O5, VO2, and V2O3 are illustrated by the characterization of the electrochromic properties of V2O5 films, a discussion about the metal to insulator transition of VO2 on the basis of in situ measurements versus temperature of its electrical and optical properties, and the characterization of the magnetic transition of V2O3 powder from SQUID measurements. For the latter compound, the influence of the crystallite size on the magnetic properties is discussed