Effect of Co Content Upon the Bulk Structure of Sr- and Co-doped LaFeO3
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The bulk structure was investigated for Fe-based perovskite-type oxides with the formula La0.6Sr0.4CoyFe1−yO3−δ (y = 0.1, 0.2, and 0.3). The materials were confirmed to be stoichiometric with respect to oxygen under ambient conditions and the structural features were then further characterized under different environments as a function of temperature. Under reducing atmospheres, the degree of reduction increased with Co content, suggesting the presence of preferential oxidation of Fe over Co. Under milder conditions, oxygen vacancy formation was not proportional to Co content, which was likely caused by an electronic structure transition. The unit cell parameters were also shown to strongly depend upon Co content, temperature, and environment. A rhombohedral to cubic transition occurred at lower temperatures for higher Co content, but showed less dependence upon environment. A change in the thermal expansion behavior occurred at the temperature where oxygen vacancies formed leading to two regions of linear thermal expansion. The use of lattice parameters compared to dilatometry allowed for the simultaneous monitoring of unit cell symmetry and expansion behavior so the link between thermal properties and unit cell symmetry could be firmly established.
KeywordsPerovskite-type oxides High temperature phase transition In-situ XRD Oxygen nonstoichiometry
The financial support provided for this work by the Ohio Coal Development Office and the Ohio Department of Development through a Wright Center of Innovation is gratefully acknowledged. The authors also thank Rick B. Watson for technical assistance in the initial stages of this research.