Chessboard/Diamond Nanostructures and the A-site Deficient, Li1/2–3x Nd1/2+xTiO3, Defect Perovskite Solid Solution

The crystal chemical origin of nanoscale chessboard/diamond ordering in perovskite-related solid solutions of composition Li0.5–3xNd0.5+xTiO3 (LNT, x ∼ 0.02–0.12) is investigated. Experimental and simulated scanning transmission electron microscopy (STEM) images are found to be consistent with the compositional modulation model proposed by previous authors. However, these earlier models do not satisfactorily explain other features observed in high-resolution STEM and TEM images, such as the two-dimensional {100} lattice fringes with the same periodicity, √2ap × √2ap, as the local LNT unit cell viewed along the [001] direction (where ap is the parent perovskite unit cell parameter). Based on bond valence sum calculations, we propose a new set of crystal structures for LNT in which Li ions are primarily bonded to only two O ions, and order one-dimensionally with √2ap periodicity. Bright-field STEM image simulations performed for this new model reproduced the experimentally observed √2ap lattice fringes, thu...

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