Cécile Rossignol

Elaboration of thin and dense CGO films adherent to YSZ by electrostatic spray deposition for IT-SOFC applications

The aim of this work was to fabricate a dense and thin film of gadolinium doped ceria (CGO) adherent on yttria-stabilized zirconia (YSZ) using electrostatic spray deposition (ESD) for intermediate temperature solid oxide fuel cells (IT-SOFC) applications. In order to optimize the film microstructure and thickness, several ESD parameters were studied such as the total salt concentration of the solution (0.05, 0.01 and 0.005 mol L−1), the substrate temperature (range from 275 to 350 °C), the solvent composition (using different butyl-carbitol : ethanol ratios), nozzle-to-substrate distance (35 and 45 mm), the solution flow rate (0.50, 0.67 and 1 mL h−1) and the deposition time (from 15 to 60 min). The different morphologies observed by SEM are discussed. A continuous 85 nm film was successfully deposited on a YSZ substrate for the first time by ESD. Grazing incidence X-ray diffraction analysis showed two phases: the cubic CGO and YSZ phases with no secondary phases. The first impedance measurements did not show any degradation of CGO/YSZ electrical properties compared with pure YSZ.

Synthesis and Structural, Electrical, and Magnetic Properties of New Iron–Aluminum Alluaudite Phases β-Na2Ni2M(PO4)3 (M = Fe and Al)

Herein we report the studies of different physical properties (structural, magnetic, thermal, morphologic, electrical, and electrochemical) of two new allotropic β-Na2Ni2M(PO4)3 (NNMP) phosphates, with M = Fe and Al. Pure orthorhombic single-phase powders were prepared under air, using an autocombustion synthesis method. They crystallize in the orthorhombic Imma space group with similar unit cell parameters [a = 10.1592(2), b = 13.0321(3), c = 6.4864(2) Å] and [a = 10.3993(1), b = 13.1966(1), c = 6.4955(1) Å] for β-Na2Ni2M(PO4)3 (NNAP) and β-Na2Ni2Fe(PO4)3 (NNFP), respectively. Crystal structures of both compounds were determined using X-ray powder diffraction and Rietveld method refinements, which indicate the occurrence of Ni2+ in the 8g site, and of M3+ in the 4a site of the structure. The structure consists of a three-dimensional anionic framework obtained by the association on MO6, NiO6, and PO4 polyhedra, sharing edges and corners. The resulting three-dimensional structure creates monodimensional channels along the [100] and [010] directions formed by face-shared oxygen polyhedra and occupied by Na+ cations. This nondisordered cationic distribution is confirmed by a significant change of magnetic properties. Thus, both NNAP and NNFP samples show paramagnetic to ferromagnetic transition at 14 and 19 K, respectively. For the two compounds, thermal stability, electrical conductivity, and electrochemical properties have been also investigated. The intercalation/desintercalation properties of NNMP compounds as positive electrode were tested in sodium-ion batteries. The first cycling curves exhibit a significant polarization for both prepared samples.