Solid solution limits and electrical properties of scheelite SryLa1-yNb1-xVxO4-delta materials for x=0.25 and 0.30 as potential proton conducting ceramic electrolytes


The proton conductivity and solid solubility limits of acceptor strontium doped vanadium stabilised lanthanum niobate (SryLa1-yNb1-xVxO4-delta, x = 0.25, 0.30 and y = 0 to 0.10) were explored as potential proton conducting ceramic electrolytes. All samples were synthesized via a solid-state method. The phase purity, microstructure and thermal expansion behaviour of the materials were studied using powder X-ray diffraction, scanning electron microscopy and dilatometry, respectively. A maximum solid solution limit of 5% Sr in the A-site of SryLa1-yNb1-xVxO4-delta samples is observed for a vanadium content of x = 0.25, while further increases in the Sr or vanadium contents lead to the presence of Sr-3(VO4)(2) as a secondary phase. This acceptor dopant content of 5%Sr in the current scheelite material exceeds that possible in the parent vanadium-free fergusonite SryLa1-yNbO4-delta material by a factor of 5. All Sr doped scheelite materials show linear thermal expansion behaviour, successfully avoiding the scheelite to fergusonite structural phase change during thermal cycling. The average grain size is shown to be increased by increasing vanadium content. In humid conditions, all phase pure samples show predominantly proton conductivity at lower temperatures, while p-type conductivity is noted at higher temperatures under dry oxidising conditions. In the low temperature range, the Sr0.05La0.95Nb0.75V0.25O4-delta sample, containing the largest acceptor dopant concentration, exhibits slightly higher bulk and specific grain boundary conductivities in comparison to other phase pure compositions. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.




Chemistry; Electrochemistry; Energy & Fuels


Brandao, AD; Nasani, N; Yaremchenko, AA; Kovalevsky, AV; Fagg, DP

nossos autores


This research work was supported by the FCT, project grant PTDC CTM-ENE/6319/2014, UID/CTM/50011/2013, the FCT Investigator Programme, projects IF/01344/2014/CP1222/CT0001, IF/01072/2013/CP1162/CT0001 and IF/00302/2012, QREN, FEDER and COMPETE Portugal and the European Union.

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