Structure, Stoichiometry, and Phase Purity of Calcium Substituted Lanthanum Manganite Powders

✍ Scribed by S. Faaland; K.D. Knudsen; M.-A. Einarsrud; L. Rørmark; R. Høier; T. Grande

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 690 KB
• Volume: 140
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7894

✦ Synopsis

Calcium-doped lanthanum manganite La 1-x Ca x MnO 3 , synthesized by the glycine/nitrate method, was characterized by high resolution synchrotron X-ray powder diffraction, electron diffraction, and infrared spectroscopy. A strong correlation was observed between the cooling rate from the calcination temperature and the powder quality, indicating the importance of a homogeneous oxygen stoichiometry. The structure refinement reveals that La 1-x Ca x MnO 3 with x ‫؍‬ 0.2, 0.3, 0.4, and 0.6 has orthorhombic symmetry with space group Pnma. The MnO 6 octahedra are fairly symmetrical, but the octahedra are tilted about 20°°relative to the ideal perovskite structure. Infrared spectroscopy revealed that only the O-Mn-O bending mode is significantly influenced by the substitution of La with Ca. In La 0.8 Ca 0.2 MnO 3 we found diffraction evidence of a superstructure in domains in some of the grains. We propose that the superstructure in La 0.8 Ca 0.2 MnO 3 is due to ordering of Ca 2؉ ions on A (La 3؉ ) sites in the perovskite ABO 3 structure.