Thermal expansion behavior and chemical compatibility of BaxSr1-xCo1-yFeyO3-δ with 8YSZ and 20GDC

Perovskite oxides of the composition BaxSr1-xCo1-yFeyO3-delta(BSCF) were synthesized via a modified Pechini method and characterized by Xray diffraction, dilatometry and thermogravimetry. Investigations revealed that single-phase perovskites with cubic structure can be obtained for x <= 0.6 and 0.2 <= y <= 1.0. The as-synthesized BSCF powders can be sintered in several hours to nearly full density at temperatures of over 1180 degrees C. Thermal expansion curves of dense BSCF samples show nonlinear behavior with sudden increase in thermal expansion rate between about 500 degrees C and 650 degrees C, due mainly to the loss of lattice oxygen caused by the reduction of Co4+ and Fe4+ to lower valence states. Thermal expansion coefficients (TECs) of BSCF were measured to be 19.2-22.9 x 10(-6) K-1 between 25 degrees C and 850 degrees C. Investigations showed further that Ba0.5Sr0.5Co0.8Fe0.2O3-delta is chemically compatible with 8YSZ and 20GDC for temperatures up to 800 degrees C, above which severe reactions were detected. After being heat-treated with 8YSZ or 20GDC for 5 h above 1000 degrees C, Ba0.5Sr0.5Co0.8Fe0.2O3-delta was completely converted to phases like SrCoO3-delta, BaCeO3, BaZrO3, etc. (c) 2006 Published by Elsevier B.V.