The substitution effect of ca in the srfeo2.5 matrixfrom a structural and dynamic viewpoint

Abstract

In the way to develop a solid oxide fuel cells (SOFC), one of the important devices that transform a chemical reaction energy (e.g. H2 + O2) directly into electrical energy, the researchers are going now in the direction to decrease the operation temperature of SOFCs from 800-1000°C to more moderate temperature around 500°C.In this context, the deficient perovskites SrMO3- (M=Fe,Co) with Brownmillerite structure type, are known as candidate materials with the highest oxygen conductivity [1-4]. Also, SrFeO2.5 is able to intercalate oxygen by electrochemical oxidation while his homologous CaFeO2.5 does not, demonstrates that the simple existence of vacancy channels solely is unable to explain the diffusion mechanism. The understanding of the underlying mechanisms for the diffusion of oxygen in solid oxides is therefore an important issue to optimize oxygen electrolytes or membranes to serve in fuel cells.It becomes evident that also the lattice dynamics must play a decisive role. In this case, the low energy mode was found by Inelastic Neutron Scattering at 7 meV and 12 meV for SrFeO2.5 andfor CaFeO2.5 respectively at room temperature [5].We are interested in the present work to the effect of structural and dynamic changes of the network related to the partial substitution of Sr by Ca. We are success for the first time to synthesis a monophasic compounds of Ca1-xSrxFeO2.5 (0x1) with a mirror furnace. Our results are confirmed with XRD, Mössbauer, EDS and Raman spectroscopy.