Defect Chemistry, Electrical Properties, and Evaluation of New Oxides Sr2CoNb1-xTixO6-delta (0 <= x <= 1) as Cathode Materials for Solid Oxide Fuel Cells.

The perovskite series Sr2CoNb1-xTixO6-delta (0 <= x <= 1) was investigated in the full compositional range to assess its potential as cathode material for solid oxide fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing the titanium content from x = 0-1 produces both oxidation of Co3+ to Co4+ (from 0 up to 40%) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit), although each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Ti-contents lose a significant amount of oxygen upon heating above 600 K. Oxygen is partially recovered upon cooling as the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating/cooling cycles and atmospheres, produce a complicated behavior of electrical conductivity. Cathodes containing Sr2CoTiO6-delta display low ASR values, 0,13 Omega cm(2) at 973 K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC.