Reply to 'Nanoscale phase separation in perovskites revisited'

Coupled Compositional and Displacive Modulations in KLaMnWO6 Revealed by Atomic Resolution Imaging

Complex compositional and displacive modulations of the crystal structure of KLaMnWO₆ are imaged with atomic resolution by means of scanning transmission electron microscopy (STEM). This oxide is stabilized by cation vacancies leading to a La_1+x/3K_1-xMnWO₆ stoichiometry. Compositional modulation on both the K and La layers are revealed in the high-angle annular dark-field STEM (HAADF-STEM) images. The compositional modulation within the La layer is coupled with the modulation of the octahedral tilting, which is exposed by imaging of the anion sublattice in annular bright-field STEM (ABF-STEM) images. These complex modulations are accommodated in a 5√2a_p × 5√2a_p × 2a_p perovskite-type structure.

Direct mapping of Li-enabled octahedral tilt ordering and associated strain in nanostructured perovskites

Self-assembled nanostructures with periodic phase separation hold great promise for creating two- and three-dimensional superlattices with extraordinary physical properties. Understanding the mechanism(s) driving the formation of such superlattices demands an understanding of their underlying atomic structure. However, the nanoscale structural fluctuations intrinsic to these superlattices pose a new challenge for structure determination methods. Here we develop an optimized atomic-level imaging condition to measure TiO6 octahedral tilt angles, unit-cell-by-unit-cell, in perovskite-based Li(0.5-3x)Nd(0.5+x)TiO3, and thereby determine the mathematical formula governing this nanoscale superstructure. We obtain a direct real-space correlation of the octahedral tilt modulation with the superstructure geometry and lattice-parameter variations. This reveals a composition-dependent, self-ordered octahedral superlattice. Amazingly, we observe a reversible annihilation/reconstruction of the octahedral superlattice correlated with the delithiation/lithiation process in this promising Li-ion conductor. This approach to quantify local octahedral tilt and correlate it with strain can be applied to characterize complex octahedral behaviours in other advanced oxide systems.