Local Atomic Structures for Tunable Ordered Arrangements of Crystallographic Shear Planes in Titanium-Chromium Oxide Natural Superlattices

The atomic structure of titanium-chromium oxide natural superlattices with different compositions having an ordered arrangement of crystallographic shear (CS) planes was investigated by high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and electron diffraction, using polycrystalline ceramics prepared by arc-melting and heat treatment. Analysis of the electron diffraction patterns revealed that not only the interspacing but also the direction of planar faults changed depending on the chromium concentration. HAADF-STEM observations showed that the atomic arrangements of CS planes deviating from (121)rutile are random arrangements of (121)rutile CS planes and (011)rutile antiphase boundaries. Using a random walk model and by calculating the specularity parameter, we found that the CS planes in titanium-chromium oxides behave as coherent interfaces for phonons based on the estimation of interface roughness.