abstract
Phase relationships, transport properties and thermomechanical behavior of acceptor- and donor-co-substituted Gd2Ti2O7 were studied for possible application in solid oxide fuel cell anodes. The range of (Gd1-xCax)(2)(Ti1-yMoy)(2)O7-delta solid solutions with a cubic pyrochlore-type structure was found to be limited to 0.10 < x < 0.15 and 0.05 < y < 0.10 under oxidizing conditions. No evidence of phase instability of substituted materials was detected in the course of the electrical and thermogravimetric studies down to oxygen partial pressures as low as 10(-19) atm at 950 degrees C. (Gd1-xCax)(2)(Ti1-yMoy)(2)O7-delta ceramics possess moderate thermal expansion coefficients compatible with solid electrolytes, (10.5-10.7) x 10(-6) K-1 at 25-1100 degrees C in air, and demonstrate remarkable dimensional stability with nearly zero chemical expansion down to p(O-2) x 10(-1)2 atm at 950 degrees C. Though co-substitution by Mo suppresses oxygen-ionic conduction under oxidizing conditions, reducing oxygen partial pressure increases both ionic and n-type electronic transport. (Gd1-xCax)(2)(Ti0.95Mo0.05)(2)O7-delta (x = 0.07-0.10) pyrochlores are mixed conductors under SOFC anode operation conditions, but comparatively low total conductivity limits its applicability as electrode materials.
keywords
OXIDE FUEL-CELL; ELECTRICAL-PROPERTIES; OXYGEN; ANODE; TRANSPORT; DISORDER; STABILITY; MIGRATION; CERAMICS; DOPANTS
subject category
Chemistry
authors
Zakharchuk, K; Kravchenko, E; Fagg, DP; Frade, JR; Yaremchenko, AA
our authors
Aleksey Yaremchenko
Principal Researcher
Jorge Ribeiro Frade
Retired Professor
Kiryl Zakharchuk
PhD StudentProjects
acknowledgements
This work was done within the scope of projects IF/01072/2013/CP1162/CT0001, IF/01344/2014 and project CICECO-Aveiro Institute of Materials POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.