Abstract
The nominal composition of Sr{sub 0.39}CoO{sub 2}, prepared by a low-temperature ion exchange technique, has been systematically studied by transmission electron microscopy, energy dispersive x-ray spectroscopy (EDX), and electron-energy-loss spectroscopy (EELS). Besides a well-defined {radical}(3)a{sub p}x{radical}(3)a{sub p} modulated structure, a series of long periodic modulated structures (n{radical}(3)a{sub p}x3a{sub p}) was revealed by high-resolution transmission electron microscopy (HRTEM) in some microzones, which are induced by alternate position ordering of strontium ions. The results of EDX analyses confirm the variation of Sr content in corresponding modulated phases. Moreover, the L{sub 3}/L{sub 2} intensity ratio of Co-L{sub 2,3} edges in the EELS spectra indicates the variation of Co ionic valence state induced by the different contents of Sr cations. Based on the {radical}(3)a{sub p}x{radical}(3)a{sub p} superstructural model, we propose the possible corresponding structural models in this paper. The simulated HRTEM images, based on those models, are consistent with experimental ones. In addition, several phase separations and some structural defects were observed in the sample.
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