A Study of the Microstructure of La1-xCaxMnO3 (x=0.5, 0.8) Solid Solutions

HREM and XPD methods are used to study the microstructure of La1-xCaxMnO3 perovskite-like oxides synthesized by pyrolysis of polymer-salt compositions. The XPD data show that the samples studied are single-phase solid solutions. Morphological transitions are observed in series of samples depending on the substitution parameter x. At 0 <= x <= 0.4 the samples can be characterized by rhombic symmetry ( space group Pnmb); at 0.5 <= x <= 0.8 the symmetry increases to the tetragonal space group 14/mmm; at 0.9 <= x <= 1 the symmetry lowers to the monoclinic space group P1121. Heating of samples with x = 0.5 and 0.8 up to 1200 degrees C in air does not lead to noticeable changes in the sample structure, which indicates their high thermal stability. When the La0.2Ca0.8MnO3 sample is heated to 1100 degrees C in vacuum nanocrystalline states with particle disintegration into microphases of different structures form because of a partial decomposition of the solid solution. As a result, a system of Mn3O4 nanoparticles appears, which is coherently bound with the perovskite phase of a defective structure.