In this work, we have used nickel nanoparticles to improve proton conductivity of the electrolyte BaCe0.9Y0.1O3−δ (BCY). Ni nanoparticles were dissolved into the compounds as their oxidized form (BaCe0.9–x Y0.1Ni x O3−δ) and precipitated upon heating under a reducing atmosphere. Below 700 °C, proton conductivity is enhanced under a reducing atmosphere. An increase of 1 order of magnitude, with respect to BCY, was observed for BaCe0.7Y0.1Ni0.2O3−δ (1.7 × 10–2 S/cm at 500 °C). This phenomenon is more pronounced for the compounds containing more nickel on the surface, which can facilitate the dissociation of hydrogen and the incorporation of protons in the structure. Under reducing atmosphere, nickel doping enhances both bulk and grain boundaries conductivities and the blocking effect appear at lower temperature.

When several classifiers are brought to contribute to the same task of recognition, various strategies of decisions, implying these classifiers in different ways, are possible. A first strategy consists in deciding using different opinions: it corresponds to the combination of classifiers. A second strategy consists in using one or more opinions for better guiding other classifiers in their training stages, and/or to improve the decision-making of other classifiers in the classification stage: it corresponds to the cooperation of classifiers. The third and last strategy consists in giving more importance to one or more classifiers according to various criteria or situations: it corresponds to the selection of classifiers. The temporal aspect of Pattern Recognition (PR), i.e. the possible evolution of the classes to be recognized, can be treated by the strategy of selection.

Metal fluorides with 3D open structures, pyrochlore (pyr) or hexagonal tungsten bronze (HTB), are promising materials as positive electrodes for rechargeable batteries or catalysts. Herein, we have developed a two-step synthesis procedure to obtain new anhydrous mixed-metal-cation fluorides crystallizing in the pyrochlore structure. The first step consists of preparing mixed-metal ammonium fluorides (NH4)­M2+Fe3+F6 (M = Mn, Fe, Co Ni) using different synthesis strategies. For M = Mn, three allotropic varieties of (NH4)­Mn2+Fe3+F6 are obtained; two phases adopt the expected pyrochlore network with either the cubic Fm3̅m or the orthorhombic Pnma space group, and the third phase exhibits a 3D network with narrow pseudotriangular cavities. 57Fe Mössbauer spectrometry indicates that the crystal structures are governed by the Fe3+/Mn2+ cationic order or disorder. The second step is a topotactic oxidation of pyr-(NH4)­M2+Fe3+F6 under a molecular F2 flow. To better understand the reaction mechanism, the topotactic oxidation was followed by thermogravimetry, XRD, FTIR, and Mössbauer spectrometry. The successful synthesis of the first anhydrous pyr-M3+ 0.5Fe0.5F3 provides a new route to prepare anhydrous mixed-metal fluorides pyrochlore with empty cavities of the open framework.