ORDERED LA(SR)-DEFICIENT NONSTOICHIOMETRY IN LA0.8SR0.2MNO3 OBSERVED BY HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

High-resolution transmission electron microscopy (HREM) was used to identify a La(Sr)-deficient ordered nonstoichiometry in perovskite-like La0.8Sr0.2MnO3 which is used in solid oxide fuel cell technology. Experimental 400 kV HREM images were recorded in the crystal projections [112] and [110] with the objective lens defocused to Delta f = -40 nm and Delta f = -185 nm. They show very good agreement with simulated images which are based on an ideal perovskite structure with 12.5 +/- 5% of the La(Sr) atoms being deficient on every second {111} plane. The actual rhombohedral distortion of La0.8Sr0.2MnO3 alone, as determined by X-ray diffraction, is not responsible for the observed HREM image contrasts. In addition, possible ordering of the strontium atoms could be excluded with the help of image simulations. (C) 1995 Academic Press,Inc.