Thermodynamic Quantities and Defect Structure of La0.6Sr0.4Co1−yFeyO3−δ(y=0–0.6) from High-Temperature Coulometric Titration Experiments
✍ Scribed by M.H.R. Lankhorst; J.E. ten Elshof
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 366 KB
- Volume
- 130
- Category
- Article
- ISSN
- 0022-4596
No coin nor oath required. For personal study only.
✦ Synopsis
The partial energies and entropies of O 2 in perovskite-type oxides La 0.6 Sr 0.4 Co 1؊y Fe y O 3؊ ( y ؍ 0, 0.1, 0.25, 0.4, 0.6) were determined as a function of nonstoichiometry by coulometric titration of oxygen in the temperature range 650-950°C. An absolute reference value of was obtained by thermogravimetry in air. The nonstoichiometry at a given oxygen pressure and temperature decreases with iron content y. At low nonstoichiometries the oxygen chemical potential decreases with . The observed behavior can be interpreted by assuming random distribution of oxygen vacancies, an electronic structure with both localized donor states on Fe, and a partially filled itinerant electron band, of which the density of states at the Fermi level scales with the Co content. The energy of the Fe states is close to the energy at the Fermi level in the conduction band. The observed trends of the thermodynamic quantities can be interpreted in terms of the itinerant electron model only when the iron content is small. At high values of the chemical potential of O 2 becomes constant, indicating partial decomposition of the perovskite phase. The maximum value of at which the compositions are single-phase increases with temperature.