Abstract
In this paper we report the successful incorporation of silicon into Sr1−yCayFeO3−δ perovskite materials for potential applications as electrode materials for Solid Oxide Fuel Cells. It is observed that Si doping leads to a change from a tetragonal or orthorhombic structure (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). The structures of the phases, SrFe0.85Si0.15O3−δ, Sr0.75Ca0.25Fe0.85Si0.15O3−δ and Sr0.5Ca0.5Fe0.85Si0.15O3−δ, were analysed using neutron powder diffraction. The data confirmed the cubic unit cell, with no long range oxygen vacancy ordering. Conductivity measurements showed an improvement in the conductivity on Si doping, especially for samples with high Ca content. Composite electrodes comprising 50% Ce0.9Gd0.1O1.95 and 50% Sr1−yCay(Fe/Si)O3−δ on dense Ce0.9Gd0.1O1.95 pellets were therefore examined in air. An improvement in the area specific resistances (ASR) values is observed for the Si-doped samples with respect to the undoped samples. Thus the results show that silicon can be incorporated into Sr1−yCayFeO3−δ-based materials and can have a beneficial effect on the performance, making them potentially suitable for use as cathode material in Solid Oxide Fuel Cells (SOFC).
Highlights
Borate, phosphate and sulphate were successfully incorporated into different cathode materials such as SrCoO3Àδ, La1ÀxSrxCo0.8 Fe0.2O3Àδ, Ba1ÀxSrxCo0.8Fe0.2O3Àδ, CaMnO3 and La1ÀxSrxMnO3type materials, leading to stabilization of high symmetry structures, as well as enhancements of both the electronic conductivity and the electrode performance with respect to the parent compounds
For the Ca-end member, CaFeO3Àδ, the samples were only single phase up to x 1⁄40.05, with attempts to produce more silicon-rich compositions leading to the segregation of secondary phases, such as Ca2SiO4 (PDF 009-0351), and there was no change in the cell symmetry for this series
All the undoped samples showed some degree of oxygen ordering, for instance, the Sr end member (y1⁄40) has a tetragonal symmetry, and as we increase the calcium content the symmetry changes to orthorhombic, as the level of oxygen vacancy ordering increases
Summary
Borate, phosphate and sulphate were successfully incorporated into different cathode materials such as SrCoO3Àδ, La1ÀxSrxCo0.8 Fe0.2O3Àδ, Ba1ÀxSrxCo0.8Fe0.2O3Àδ, CaMnO3 and La1ÀxSrxMnO3type materials, leading to stabilization of high symmetry structures, as well as enhancements of both the electronic conductivity and the electrode performance with respect to the parent compounds. In a recent work we have extended such studies to SrFeO3Àδ, which is an interesting material that exhibits both high mixed oxide ionic and high electronic conductivity and can be potentially used in electrochemical devices such as oxygen permeation membranes, and SOFCs [31,32,33]. Iron cations in this system have a mixed valence state with an average oxidation state between þ 4 to þ3, corresponding to a wide range of oxygen nonstoichiometry. Such phases have been traditionally thought to require very high pressure synthesis conditions, and so the work here, showing the synthesis of a range of Fe and Si containing perovskite at ambient pressure, is of significant relevance to the perovskite chemistry field in general, indicating that the ability of the perovskite structure to accommodate Si is far more widespread than initially believed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
