Determination of proton- and oxide ion tracer diffusion in lanthanum tungstate (La/W = 5.6) by means of ToF-SIMS

Ragnhild Hancke; Sarah Fearn; John A. Kilner; Reidar Haugsrud

doi:10.1039/C2CP42278F

Determination of proton- and oxide ion tracer diffusion in lanthanum tungstate (La/W = 5.6) by means of ToF-SIMS

Ragnhild Hancke,^a Sarah Fearn,^b John A. Kilner^b and Reidar Haugsrud*^a

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* Corresponding authors

^a Department of Chemistry, University of Oslo, FERMiO, Gaustadalléen 21, Norway

^b Department of Materials, Imperial College London, Prince Consort Road, London SW7 2BP, UK
E-mail: reidar.haugsrud@smn.uio.no
Fax: +44 (0)47-22840651
Tel: +44 (0)47-22840659

Abstract

Tracer diffusion of protons and oxide ions, as well as chemical diffusion of water, have been determined for the high temperature proton conductor lanthanum tungstate by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). The oxygen tracer diffusion and surface exchange coefficients, Image ID:c2cp42278f-t1.gif and Image ID:c2cp42278f-t2.gif , were measured after exchange anneals in water vapor enriched in H₂¹⁸O between 350 and 620 °C, and the apparent activation energies were 176 and 82 kJ mol⁻¹, respectively. The hydrogen tracer diffusion coefficient ( Image ID:c2cp42278f-t3.gif ) was measured between 220 and 320 °C after exchange anneals in D₂O-containing atmospheres, and the apparent activation energy was 63 kJ mol⁻¹. The extracted Image ID:c2cp42278f-t4.gif agrees with the results of transient conductivity- and TG-measurements. Chemical diffusion and surface exchange coefficients, Image ID:c2cp42278f-t5.gif and Image ID:c2cp42278f-t6.gif , were measured at 250 and 400 °C, and the result confirms that the material is hydrated by ambipolar sluggish transport of protons and oxide ions. The surface exchange coefficients were compared to the result of TG relaxation, suggesting that access to oxygen vacancies limits the overall surface exchange reaction under incorporation of water and oxygen.

Article information

https://doi.org/10.1039/C2CP42278F

Article type

Paper

Submitted

04 Jul 2012

Accepted

29 Aug 2012

First published

30 Aug 2012

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Phys. Chem. Chem. Phys., 2012,14, 13971-13978

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Determination of proton- and oxide ion tracer diffusion in lanthanum tungstate (La/W = 5.6) by means of ToF-SIMS

R. Hancke, S. Fearn, J. A. Kilner and R. Haugsrud, Phys. Chem. Chem. Phys., 2012, 14, 13971 DOI: 10.1039/C2CP42278F

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Physical Chemistry Chemical Physics

Determination of proton- and oxide ion tracer diffusion in lanthanum tungstate (La/W = 5.6) by means of ToF-SIMS

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Determination of proton- and oxide ion tracer diffusion in lanthanum tungstate (La/W = 5.6) by means of ToF-SIMS

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