Transmission electron microscopy studies of NaLaMgWO6: spontaneous formation of compositionally modulated stripes |
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Authors: | García-Martín Susana Urones-Garrote Esteban Knapp Meghan C King Graham Woodward Patrick M |
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Institution: | Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense, Madrid-28040, Spain. sgmartin@quim.ucm.es |
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Abstract: | Transmission electron microscopy studies of the perovskite NaLaMgWO 6 reveal the formation of a complex, compositionally modulated structure. Annular dark field scanning transmission electron microscopy images and scanning transmission electron microscopy-electron energy-loss spectroscopy scans show that this modulation involves a repeating pattern of La-rich and La-poor stripes, each stripe 6 a p or approximately 24 A wide (where a p is the edge length of the simple cubic perovskite unit cell). High-resolution transmission electron microscopy images clearly show, and electron diffraction patterns confirm, a periodicity of 12 a p along either the 100] p or 010] p direction. Available evidence suggests a spontaneous separation into stripes that possess the nominal stoichiometry, NaLaMgWO 6, alternating with Na-poor/La-rich stripes that have a stoichiometry of (La x Na 1-3 x )LaMgWO 6. X-ray powder diffraction measurements are insensitive to this intricate structural complexity, which may be a more widespread feature of (A (+)Ln (3+))MM'O 6 perovskites than previously appreciated. |
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