282639 Insights Into Ion Transport Pathways in Ceramics by in-Situ Neutron Diffraction

Monday, October 29, 2012: 3:40 PM
402 (Convention Center )
Steven McIntosh1, Rosemary Cox-Galhotra2, Ashfia Huq3 and Jason Hodges3, (1)Chemical Engineering, Lehigh University, Bethlehem, PA, (2)Department of Chemical Engineering, University of Virginia, Charlottesville, VA, (3)Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN

The search for higher conductivity materials for solid oxide fuel cell (SOFC), and ceramic ion-transport membranes (ITMs) is increasingly leading towards more crystallographically complex materials. The traditional materials palette is based on a cubic perovskite structure, with randomly distributed oxygen anion vacancies. Ion transport, which occurs by ion hopping between these sites, is thus directionally homogenous. In contrast, the oxygen anion vacancies in higher order layered-perovskite materials are suggested to be localized within channels or planes within the crystal structure, leading to localization and heterogeneity in the ion transport pathway.

Powder neutron diffraction provides an ideal tool to examine the bulk structure of these materials. Unlike X-ray diffraction, where X-rays interact only weakly with oxygen atoms, neutron diffraction provides information on the position, occupancy, and thermal motion of both the cations and oxygen anions in the materials of interest. This enables the oxygen non-stoichiometry, lattice expansion, and preferred anion transport pathways to be determined in a single experiment. Since these parameters vary with temperature and gas atmosphere, it is necessary to perform these measurements at in-situ conditions.

We will present recent insights into the preferred ion transport pathways in layered perovskites as determined by neutron diffraction between 550 and 825oC at pO2 from 10-1 to 10-4 atm.

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