Discommensuration of doped [Ca ₂CoO ₃] _p CoO ₂

Single-crystal x-ray diffraction and high-resolution electron microscopy studies were carried out for Co-121 ([Ca ₂CoO ₃] _p CoO ₂) and Sr-doped Co-121 grown in a KCl flux at 810°C. Typically, the samples were 2 mm × 2 mm × 0.02 mm in size. The single-crystal diffraction intensities were measured by the use of a four-circle diffractometer. Twinned super reflections, e.g., 010\bar{1}/0\bar{2}04 and 020\bar{2}/0\bar{1}03 were observed in the electron diffraction patterns. These super reflections were not observed in the end-member. Diffuse scattering was observed in the same reciprocal space by the single-crystal x-ray diffraction study. A discommensurate crystal model is proposed for the Sr-doped system.