Crystal structure and diffusion path of mixed conductors PrBa_1−xSr_xCo₂O₅₊(x= 0 and 0.5)

Abstract

Poster Sessions C497 coefficient to those of the closer components and be chemically compatible with them.SOFCs operate at high termperatures under either oxidising or reducing atmospheres over a long period of time. This can create different problems such as interface reactions which could promote the formation of insulating phases, limiting their long-term stability [1]. In light of this, the idea is to find new materials that are very stable at high temperatures and have the properties described above.Here we report the investigation of the family of pyrochlores of general formula A 2 B 2 O 7 (where A is a trivalent ion, usually a rare earth, and B is a tetravalent ion) which are known to exhibit oxygen ion conductivities of the order of 10-2 S/cm at 1000 º C, making them promising candidates as electrolytes. In particular we have focused on Ln 2 Zr 2 O 7 (Ln= Lanthanide) whose structure is mainly governed by the ion size difference between Ln 3+ and Zr 4+ [5]. These materials have the properties needed to be a good electrolyte (high melting point, high thermal expansion coefficient, low thermal conductivity, high thermal stability and high electrical conductivity) in SOFCs [6]. Among the rare earth zirconates, Ce 2 Zr 2 O 7 bears additional interest due to the catalytic application of the CeO 2 -ZrO 2 in several chemical processes in industry and automobiles [7].We have study the stability in air of the solid solutions La 2 -x Ce x Zr 2 O 7 and Gd 2-x Ce x Zr 2 O 7 and the effect of the Ce-doping on the conductivity. The X-ray diffraction studies show, that the La-series keeps the pyrochlore structure up to x = 0.5, while the Gd one adopts the fluorite structure. These results will be correlated to the conductive behavior of these materials.[ Mixed oxide-ionic and electronic conducting ceramics (MIECs) will become increasingly important for future environmentally friendly ("green") societies, because the MIECs are used as materials for oxygen separation membranes and cathodes of solid-oxide fuel cells (SOFCs). Oxygen is an important reactant in the industrial chemical processes and air is usually utilized as the oxygen source due to the cost problem. For lower temperature devices, novel MIECs with higher oxide-ion diffusivity are required. For this purpose, it is of vital importance to investigate the oxide-ion diffusion mechanism at an atomic scale. Bourgogne, 21078 Dijon, b ESRF, 38043 Grenoble (France). E-mail: ioana.popa@u-bourgogne.fr Low chromium ferritic steels have been extensively studied for applications in power generating plant life time. Formation of dense, thick, and adherent chromia (Cr 2 O 3 ) layer on stainless steel, which is considered like a good way to increase the oxidation resistance, is closely related to many parameters such as chromium content, temperature, oxidizing atmosphere, cycles frequency and time of exposure [1][2][3]. For grades with 9%Cr such as T/P91, the chromium content is not enough to fulfil the protective action by creating a continuous chromia scale over 600°C. As...