| Sumario: | Transmission electron microscopy studies of the perovskite NaLaMgWO[sub6] 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 6a[subp] or ∼24 Å wide (where a[subp] 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 12a[subp] along either the [100][subp] or [010][subp], direction. Available evidence suggests a spontaneous separation into stripes that possess the nominal stoichiometry, NaLaMgWO[sub6], alternating with Na-poor/La-rich stripes that have a stoichiometry of (La[subx]Na[sub1-3x])LaMgWO[sub6]. X-ray powder diffraction measurements are insensitive to this intricate structural complexity, which may be a more widespread feature of (A[sup+]Ln[sup3+])MM'O[sub6] perovskites than previously appreciated.
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