abstract
The high-temperature scheelite phase of Sr0.02La0.98NbO4 materials has been retained to room temperature via vanadium substitution for the Sr0.02La0.98Nb1-xVxO4-delta compositional range of 0.25 <= x <= 0.325. Such structural stabilization avoids the characteristic break in the thermal expansion coefficient (TEC) that may otherwise be deleterious for the application of LaNbO4-based materials as proton-conducting electrolytes. The transport properties of composition Sr0.02La0.98Nb0.7V0.3O4-delta have been extensively characterized. The composition offers pure proton conduction with higher conductivity than the base composition Sr0.02La0.98NbO4-delta in the low-temperature range under wet oxidizing conditions. A wide ionic domain is observed, which increases as the temperature decreases. Suggested operational limits have been documented. Under dry oxidizing conditions, vanadium substitution is shown to suppress p-type conductivity, in comparison to the base composition Sr0.02La0.98NbO4-delta. In contrast, under wet conditions, Sr0.02La0.98Nb0.7V0.3O4-delta, is observed to be a pure proton conductor in oxygen and argon atmospheres at temperatures lower than similar to 700 degrees C. The total ionic conductivity equals that of the proton conductivity, within experimental error, suggesting negligible oxide-ion conduction in this material under these conditions.
keywords
TRANSPORT NUMBER DETERMINATION; FUEL-CELLS; POWDER DIFFRACTION; EMF-MEASUREMENTS; DOPED LANBO4; OXIDES; TRANSITIONS; STABILITY; BEHAVIOR; SYSTEM
subject category
Chemistry; Materials Science
authors
Brandao, AD; Antunes, I; Frade, JR; Torre, J; Kharton, VV; Fagg, DP
our authors
Isabel Alexandra Gonçalves Antunes
Junior Researcher
Jorge Ribeiro Frade
Retired Professor
José António Perez de la Torre
Post-doc Fellowship
Vladislav Kharton
Invited Principal Researcheracknowledgements
This work was supported by the FCT, Portugal (through Grant Nos. PTDC/CTM/64357/2006, FCT, SFRH/BD/60265/2009, FCT, PTDC/CTM/105424/2008, PTDC/CTM/100412/2008).