Crystal structure, morphology and physical properties of LaCo1−xTixO3±δ perovskites prepared by a citric acid assisted soft chemistry synthesis
✍ Scribed by Rosa Robert; Dmitry Logvinovich; Myriam H. Aguirre; Stefan G. Ebbinghaus; Laura Bocher; Petr Tomeš; Anke Weidenkaff
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 760 KB
- Volume
- 58
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
The influence of the partial substitution of Co by Ti in the LaCoO 3 perovskite system is studied by evaluating the electrical conductivity, the Seebeck coefficient and the thermal conductivity of the compounds up to T = 1273 K. The X-ray diffraction patterns of the LaCo 1Àx Ti x O 3±d (0.01 6 x 6 0.5) phases show two structural modifications depending on the Ti content. Compounds with x < 0.3 crystallize in the rhombohedrally distorted perovskite structure while samples with x P 0.3 possess an orthorhombic unit cell. The oxidation state of the Co ions is studied by X-ray absorption near edge structure (XANES) spectroscopy. A negative thermoelectric power is found in the LaCoO 3 system for low level Ti substitution (x = 0.01). In contrast, samples with higher Ti content show a large positive Seebeck coefficient, indicating positive majority charge carriers in the system. The electrical resistivity of the studied materials reveals a semiconducting-like behaviour. The lattice thermal conductivity was found to be low and nearly temperature-independent. The samples exhibit very small crystallite sizes in the range of few nanometres. Therefore, the low thermal conductivity can be assigned to an enhanced phonon scattering on grain boundaries.