Microstructure and defect investigations of the layered manganites La 2–2 x Ca 1+2 x Mn 2 O 7 ( x = 0.6, 0.8 and 0.9) by HREM

The microstructure and defects of the n = 2 Ruddlesden–Popper manganites La 2–2 x Ca 1+2 x Mn 2 O 7 ( x = 0.6, 0.8 and 0.9) were investigated by electron diffraction and high‐resolution transmission electron microscopy. Besides the predominant n = 2 layered structure in the examined compounds, intergrowths with different number of the perovskite‐like layers were observed. Intergrowth of n = 1 (K 2 NiF 4 ‐type) was observed only in x = 0.9 sample. Intergrowths with n ≥ 5, essential perovskite microdomains or inclusions, were seen in the x = 0.8 and 0.6 samples. The type of defects in x = 0.8 sample is much richer than that in x = 0.6 and 0.9 samples and two rare types were observed and analyzed. Some of edge dislocations in the x = 0.6 specimen were presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)