Synthesis and structural characterization of gadolinium barium cobalt oxide Gd<sub>8</sub>Ba<sub>5</sub>Co<sub>4</sub>O<sub>21</sub> with CoO<sub>5</sub> square pyramids

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Abstract

<p>We have determined the crystal structure of Gd8Ba5Co4O21 by single-crystal X-ray diffraction and transmission electron microscopy (TEM). Gd8Ba5Co4O21 shows a tetragonal I4/m structure with a = 13.8982(3) Å and c = 5.76510(10) Å. This compound is isostructural with R8Ba5Ni4O21 (R = rare-earth ions) with two types of BaO10, GdO7 and CoO5 polyhedra. Using scanning TEM, we directly observed the atomic arrangements of Gd8Ba5Co4O21, which was consistent with crystal structure analysis. Isolated CoO5 square pyramids are placed with the relationship to 4-fold symmetry about the c-axis. Gd8Ba5Co4O21 has a similar local structure to R2BaCoO5 with a Y2BaNiO5-type structure. The first neighboring Co–Co atomic distances are shorter than those of R2BaCoO5 because of changes in the framework structure composed of RO7 and CoO5 polyhedra.</p>

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