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Influence of synthesis route and composition on electrical properties of La9.33 + xSi6O26 + 3x/2 oxy-apatite compounds

Chesnaud, Anthony and Dezanneau, G. and Estournès, Claude and Bogicevic, Christine and Karolak, Fabienne and Geiger, S. and Geneste, G. Influence of synthesis route and composition on electrical properties of La9.33 + xSi6O26 + 3x/2 oxy-apatite compounds. (2008) Solid State Ionics, vol. 179 (n° 33 - 34). pp. 1929-1939. ISSN 0167-2738

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Official URL: http://dx.doi.org/10.1016/j.ssi.2008.04.035

Abstract

Oxy-apatite materials La9.33 + xSi6O26 + 3x/2 are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well-known difficulties related to their densification prevent them from being used as such. This paper presents strategies to obtain oxyapatite dense materials. First, freeze-drying has been optimized to obtain ultrafine and very homogeneous La9.33 + xSi6O26 + 3x/2 (0≤x≤0.67) nanopowders. From these powders, conventional and Spark Plasma Sintering (SPS) have been used leading to very dense samples obtained at temperatures rather lower than those previously reported. For instance, SPS has allowed to prepare fully dense and transparent ceramics from 1200 °C under 100 MPa. The microstructure and transport properties of such samples have been then evaluated as a function of sintering conditions and lanthanum content. It will be show that for lanthanum content higher than 9.60 per unit formula, the parasitic phase La2SiO5 appears leading to a egradation of conduction properties.We also show that grain boundaries and porosity (for conventionally-sintered materials) seem to have blocking effects on oxygen transport. The highest overall conductivity values at 700 °C, i.e. σ700 °C=7.33.10−3 S cm−1, were measured for La9.33Si6O26 material conventionally-sintered at 1500 °C which contains bigger grains' size by comparison with σ700 °C=4.77.10−3 S cm−1 for SPS-sintered materials at the same temperature but for few minutes. These values are associated with activation energies close to 0.83–0.91 eV, regardless of sintering condition, which are commonly encountered for anionic conductivity into such materials.

Item Type:Article
Additional Information:Thanks to Elsevier editor. The definitive version is available at http://www.sciencedirect.com The original PDF of the article can be found at Solid State Ionics website : http://www.sciencedirect.com/science/journal/01672738
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS
Université de Toulouse > Institut National des Sciences Appliquées de Toulouse - INSA
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
Other partners > Ecole Centrale de Paris (FRANCE)
Other partners > Université Paris-Sud 11 (FRANCE)
Laboratory name:
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Deposited By: Celine Cabaup

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