Elaboration of tin oxide nano-islands through post-deposition thermal treatment

International audienceTin dioxide (SnO2) films have been grown onto (006) sapphire substrates by sol-gel dip-coating using tin alkoxide solutions. It is shown, using transmission electron microscopy and atomic force microscopy, that the thickness of the layers is easily controlled with tin concentration. It can vary after the deposition process between few nanometers and few tens of nanometers according to the concentration of the precursor in the sol. A postdeposition thermal treatment forces the continuous precursor film to split into isolated islands. A decrease of the tin concentration in the precursor sol to 100 μM allows the formation of islands of a few nanometers (3 nm) in height and several tens of nanometers in diameter (30 nm). Such height value is very close to the Bohr radius of SnO2

Characterization of electrical conduction and nature of charge carriers in mixed and ionic conductors

International audienc

Ecoulements capillaires et chargés dans les procédés d'élaboration de composites par APS et RMI

Un procédé alternatif envisagé pour la réalisation de matériaux composites [1,2] à matrice céramique consiste à combiner un procédé APS (Aspiration Poudres Submicroniques) avec un procédé RMI (Reactive Melt Infiltration). L'étape APS consiste à assurer une première densification du composite par l'apport, par injection forcée, de nanocharges qui viennent remplir les espaces poraux entre le

Densification of Highly Defective Ceria by High Temperature Controlled Re-Oxidation

Highly enhanced densification and grain growth of Ce0.9Gd0.1O1.95-delta (CGO, gadolinium-doped ceria, with 10 mol% Gd) is achieved in low oxygen activity atmospheres. However, the material can suffer mechanical failures during cooling when the re-oxidation process-is not controlled due to-the large volume changes. In this work, the redox process of COO is investigated using dilatometry, microscopy, electrochemical impedance spectroscopy and thermodynamic analysis. In addition, the conditions allowing controlled re-oxidation and cooling in order to preserve the mechanical integrity of the CGO component are defined: this can be achieved over a wide temperature range (800-1200 degrees C) by gradually increasing the oxygen content of the atmosphere. It is found that the electrical conductivity of the COO, particularly at low temperature (<450 degrees C) is influenced by the sintering and controlled re-oxidation conditions. An increase in activation energy for conduction at low temperature is observed as the re-oxidation temperature decreases. Moreover it was observed that the ionic conductivity blocking effect, usually associated with grain boundary contributions, is not influenced by the grain size but rather by the chemical history of the material. (C) 2014 The Electrochemical Society. All rights reserved

Ecoulements capillaires et chargés dans les procédés d'élaboration de composites par APS et RMI

Un procédé alternatif envisagé pour la réalisation de matériaux composites [1,2] à matrice céramique consiste à combiner un procédé APS (Aspiration Poudres Submicroniques) avec un procédé RMI (Reactive Melt Infiltration). L'étape APS consiste à assurer une première densification du composite par l'apport, par injection forcée, de nanocharges qui viennent remplir les espaces poraux entre le

Synthesis and electrochemical characterization of lanthanum silicates as ionic conducting materials for fuell cells applications

International audienc

Study of the formation of the apatite-type phases La 9.33þx (SiO 4 ) 6 O 2þ3x/2 synthesized from a lanthanum oxycarbonate La 2 O 2 CO 3

International audiencea b s t r a c t Lanthanum silicated apatites with nominal composition La 9.33þx (SiO 4) 6 O 2þ3x/2 (À0.2 < x < 0.27) have been successfully synthesized by solid state reaction using a new reagent La 2 O 2 CO 3 and amorphous SiO 2 precursors. The formation mechanism of La 2 O 2 CO 3 reagent, which cannot be purchased, has been fol-lowed by in-situ temperature depend XRD of La 2 O 3 under CO 2 atmosphere. The stability of this reagent during the synthesis step allowed to limit the formation of secondary phase La 2 Si 2 O 7 and made the weighting of the reagent easier. High purity powders could be synthesized at the temperature of 1400 C. Dense pellets (more than 98.5%) were obtained by isostatic pressing of powders calcined at 1200 C and then sintered at 1550 C. Traces of La 2 SiO 5 secondary phase present in synthesized powder disappeared after densification and pure oxyapatite materials were obtained for all the compositions. Electrical measurements confirmed that conductivity behaviors of the sintered pellets were dependent to the oxygen over-stoichiometry. Indeed, a relatively high conductivity of 1 Â 10 À2 S cm À1 was exhibited at 800 C for the nominal composition La 9.60 (SiO 4) 6 O 2.405 with low activation energy around 0.79 eV. The ionic conductivity properties were comparable with that of the earlier obtained materials

Structural modifications of lanthanum silicate oxyapatite exposed to high water pressure

International audienceDense lanthanum silicate oxyapatite samples La9.33 + x(SiO4)6O2 + 3x/2 were exposed to high water pressure in autoclave, in order to study the effects of oxygen stoichiometry and treatment duration on the protonation of these materials. TG analyses showed that protonic species were successfully introduced into the bulk of the material, especially for La9.60(SiO4)6O2.4 sample after 84 h of treatment at 550 °C under 40 bar water pressure. It was shown that the mass loss compares well with perovskite materials and increases when protonation time rises (0.66% above 600 °C for 408 h), with a time limit beyond which the microstructure is no more stable.Rietveld refinement and Raman spectroscopy studies confirmed some structural modifications which could be linked to the incorporation of protonic species. It was shown that autoclave treatment induced an increase of the cell volume related to an increase of the a and b lattice parameters (enlargement of the characteristic channels of oxyapatite)