Crystal structure and thermal properties of La1−xSrxFeO3−δ (x= 0, 0.1, 0.3, 0.4, 0.5, and 0.75) have been studied by high‐temperature X‐ray diffraction and thermal analysis in air and nitrogen (p(O2) ∼ 10−3 atm) atmosphere. The first‐order phase transition from orthorhombic‐to‐rhombohedral La1−xSrxFeO3−δ (x= 0, 0.1) was strongly shifted to lower temperatures with increasing Sr content. The phase‐transition temperature was observed significantly lower in polycrystalline ceramics compared with fine powders. The temperature depression of the phase transition in the ceramics was qualitatively explained by stresses induced both by the anisotropic thermal expansion of LaFeO3 and the observed volume contraction of the phase transition. Rhombohedral La1−xSrxFeO3−δ (x= 0.3, 0.4, 0.5) were observed to transform to the cubic perovskite structure during heating. The second‐order phase‐transition temperature decreased with increasing Sr content and decreasing partial pressure of oxygen. On the basis of the present findings, a pseudobinary phase diagram of the LaFeO3–SrFeO3−δ system is presented. Finally, a severely nonlinear thermal expansion was observed for the Sr‐rich materials at high temperature. The high thermal expansion in this region is due to a chemical expansion resulting from a reduction of the valence state of Fe.
Electron microscopy characterization across the cathode–electrolyte interface of two different types of intermediate temperature solid oxide fuel cells (IT‐SOFC) is performed to understand the origin of the cell performance disparity. One IT‐SOFC cell had a sprayed‐cosintered Ce0.90Gd0.01O1.95 (CGO10) barrier layer, the other had a barrier layer deposited by pulsed laser deposition (PLD) CGO10. Scanning electron microscopy, transmission electron microscopy (TEM), and electron backscattered diffraction (EBSD) investigations conclude that the major source of the cell performance difference is attributed to CGO–YSZ interdiffusion in the sprayed‐cosintered barrier layer. From TEM and EBSD work, a dense CGO10 PLD layer is found to be deposited epitaxially on the 8YSZ electrolyte substrate—permitting a small amount of SrZrO3 formation and minimizing CGO–YSZ interdiffusion.
In the present paper, anode supported solid oxide fuel cells (SOFCs), produced on a pre‐pilot plant scale in ten batches of ∼100 cells, are characterised with respect to performance. The main purpose was to evaluate the reproducibility of the scaled‐up process. Based on 20 tests, the average area specific cell resistance at 850 °C was found to be 0.24 Ω cm2 with a standard deviation of 0.05 Ω cm2. The variation in performance between the cells can be largely attributed to variations in the cathode performance. Experimental evidence will be presented on full 4 × 4 cm2 cells, symmetric cells with two cathodes on a YSZ strip, and a special cell with a divided cathode.
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