ABSTRACT
New advanced fuel cell technologies are moving towards high-temperature proton conductors (HTPCs) to meet environmental issues. Their elaboration remains a challenge and micro-computed tomography (µCT) is an innovative way to control their quality. NiO-BZY anodic supports of a protonic ceramic electrochemical cell (PCEC), elaborated by co-tape casting and co-sintered at 1350 °C, were coated with a BZY20 electrolyte layer by DC magnetron sputtering. The µCT allowed to observe defects inside the volume of these PCEC half-cells and to show their evolution after an annealing treatment at 1000 °C and reduction under hydrogen. This technique consists in obtaining a 3D reconstruction of all the cross-sectional images of the whole sample, slice by slice. This allows seeing inside the sample at any desired depth. The resolution of 0.35 µm is perfectly adapted to this type of problem considering the thickness of the different layers of the sample and the size of the defects. Defects were detected, and their interpretation was possible thanks to the 3D view, such as the phenomenon of NiO grain enlargement explaining defects in the electrolyte, the effect of NiO reduction, and finally, some anomalies due to the shaping process. Ways to anticipate these defects were then proposed.
ABSTRACT
Inclined, zigzag and spiral TiAg films were prepared by glancing angle co-deposition, using two distinct Ti and Ag targets with a particle incident angle of 80° and Ag contents ranging from 20 to 75 at%. The effect of increasing Ag incorporation and columnar architecture change on the morphological, structural and electrical properties of the films was investigated. It is shown that inclined columnar features (ß = 47°) with high porosity were obtained for 20 at% Ag, with the column angle sharply decreasing (ß = 21°) for 50 at% Ag, and steeply increasing afterwards until ß = 37° for the film with 75 at% Ag. The sputtered films exhibit a rather well-crystallized structure for Ag contents ≥50 at%, with a TiAg (111) preferential growth. No significant oxidation was detected in all films, except for the one with 20 at% Ag, after two 298-473-298 K temperature cycles in air. The calculated temperature coefficient of resistivity (TCR) values vary between 1.4 and 5.5 × 10-4 K-1. Nano-sculptured spiral films exhibit consistently higher resistivity (ρ = 1.5 × 10-6 Ω m) and TCR values (2.9 × 10-4 K-1) than the inclined one with the same Ag content (ρ = 1.2 × 10-6 Ω m and TCR = 2.0 × 10-4 K-1). No significant changes are observed in the zigzag films concerning these properties. The effective anisotropy A eff at 473 K changes from 1.3 to 1.7 for the inclined films. Spiral films exhibit an almost completely isotropic behavior with A eff = 1.1. Ag-rich TiAg core + shell Janus-like columns were obtained with increasing Ag concentrations.
ABSTRACT
The present study describes a sputtering and in situ vacuum electrical resistivity setup that allows a more efficient sputtering-oxidation coupling process for the fabrication of oxide compounds like vanadium dioxide, VO2. After the sputtering deposition of pure V thin films, the proposed setup enables the sample holder to be transferred from the sputtering to the in situ annealing + resistivity chamber without venting the whole system. The thermal oxidation of the V films was studied by implementing two different temperature cycles up to 550 °C, both in air (using a different resistivity setup) and vacuum conditions. Main results show that the proposed system is able to accurately follow the different temperature setpoints, presenting clean and low-noise resistivity curves. Furthermore, it is possible to identify the formation of different vanadium oxide phases in air, taking into account the distinct temperature cycles used. The metallic-like electrical properties of the annealed coatings are maintained in vacuum whereas those heated in air produce a vanadium oxide phase mixture.
