Electrochemical behavior and performances of Ni-BaZr 0·1 Ce 0·7 Y 0.1 Yb 0.1 O 3−δ cermet anodes for protonic ceramic fuel cell

International audienceHigh performance Ni-BCZYYb cermet anode were prepared at 1300 °C using electrolyte powders prepared by combustion and commercial NiO. The cermets are porous (39 vol% of porosity), show a high electronic conductivity (1097 S cm−1) and sufficient mechanical properties. The electrochemical behavior of the Ni-BCZYYb/BZCYYb-ZnO/Ni-BCZYYb symmetrical cell elaborated by co-pressing and co-sintering was investigated using electrochemical impedance spectroscopy. The impedance spectroscopy study show that the electrode reaction involves three steps. The total polarization Area Specific Resistance decreases by about one order of magnitude when increasing the temperature from 450 to 600 °C or the H2 concentration from 5 to 100 vol% to reach 0.049 Ω cm2 at 600 °C under pure hydrogen

New Insights of the Solid State Transformations in the Ag-Se-Ge System : a Mechanical Spectroscopy Study

a study of degrees of freedom exhibited by partially crystallised material of the system Ag-Se-Ge is reported. Mechanical spectroscopy reveals 3 processes in the temperature range 250K to 330K. Two processes at 298K and 315K are assigned to solid state transformations in Ag8GeSe6 crystallites. A broad relaxation process exhibiting a high activation energy is connected to cooperative events assumed to occur in the glassy matrix. The two first processes also manifest in DSC experiments. The high temperature one is definitively attributed to allotropic transformation of Ag8GeSe6 crystalline phase. The low temperature one is reported for the first time in this paper and is attributed to the transformation of a crystalline metastable phase induced by constraints imposed by the surronding glassy matrix

The structure of ionically conductive chalcogenide glasses: A combined NMR, XPS and ab initio calculation study

cited By 8International audienceThis paper reports on the structural investigation of lithium and sodium thiosilicate crystals and glasses by means of X-ray photoelectron spectroscopy and ab initio calculation. The results are analysed in conjunction with previously reported 29Si NMR data. While NMR proved to be an effective tool for the quantitative discrimination of edge- and corner-sharing tetrahedra existing in these materials, X-ray photoelectron spectroscopy (XPS) gives information on the nature of Si-S bonds, i.e. bridging and non-bridging bonds. The main result is the noticeable difference existing between the structures of lithium and sodium thiosilicate glasses, which, according to XPS data, is due to different electronic redistributions over the network when one or the other alkali is added, the sodium addition resulting in a change in the electronic distribution over the entire network

Copper (II) selective electrode based on chalcogenide materials: study of the membrane/solution interface with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy

International audienceThe response of copper (II) ion-selective electrodes based on chalcogenide glassy–crystalline Cu–As–S alloys is described. The potentiometric measurements showed a Nernstian behavior in a large range of copper (II) concentration with short response time and a detection limit close to 1×10−6 M. The selectivity and the effect of the pH on the response have been determined. The chalcogenide membrane/solution interface has been investigated using electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) in order to understand the sensing properties

Structural characterization of amorphous SiCxNy chemical vapor deposited coatings

International audienceChemical bonding and local order around the different atoms of thick amorphous SiCxNy deposits [0.03⩽x/(x+y)⩽0.67] prepared with chemical vapor deposition at 1000–1200 °C using TMS–NH3–H2 have been investigated using x-ray photoelectron spectroscopy (XPS), Raman spectrometry, Fourier transform infrared spectrometry (FT-IR), electron energy loss spectroscopy (EELS) and 29Si magic-angle spinning nuclear magnetic resonance spectrometry (MAS-NMR). XPS analyses have shown that the main bonds are Si–C, Si–N, and C–C, and have suggested the existence of C–N bonds. According to Raman analyses and complementary FT-IR absorption of thin films, the coatings are nonhydrogenated. Si, C and N atomic chemical environments are more complicated than in a mixture of pure Si3N4–SiC phases. The examination of the Si KL2,3L2,3 line shapes recorded by XPS have allowed one to state the existence of Si(C4−nNn) units. Mixed coordination shells around silicon have been confirmed by EELS analyses. Additionally, FT-IR reflection analyses have proved that Si is both bonded with N and C. Indirect indication has been obtained owing to the 29Si MAS-NMR analyses of powders. Raman analyses have been conclusive to assume that C–C bonds correspond to a mixed sp3−sp2 carbon configuration linked with Si(C4−nNn) tetrahedra with 0⩽n⩽4