Changes in the crystal structure of layered perovskite compounds A₃B₂O₉ (A = Ba, Sr; B = W, Re)

抄録

Layered perovskite compounds exhibit various electrical properties due to their crystal structure. This review focused on the synthesis and characterization of B-cation-deficient hexagonal perovskite A₃B₂O₉ (A = Ba, Sr; B = W, Re), which exhibits two-dimensional perovskite layers and perovskite layer stacking along the [111] direction in the simple perovskite notation. Ba₃W₂O₉, Sr₃W₂O₉, and Sr₃Re₂O₉ were obtained through high-pressure synthesis. Crystal structure analysis was conducted using single crystal X-ray diffraction and transmission electron microscopy. Ba₃W₂O₉ was found to be isostructural with Ba₃Re₂O₉ and exhibited no octahedral rotation and tilt. By contrast, Sr₃W₂O₉ and Sr₃Re₂O₉ were hettotype structures of Ba₃W₂O₉ at 298 K and demonstrated phase transitions related to octahedral rotation and distortion. The substitution of Sr for Ba at the A-site induced compressive chemical pressure and crystal structure changes. The crystallographic differences between Sr₃W₂O₉ and Sr₃Re₂O₉ were octahedral tilts related to the 5d electron configuration. In A₃B₂O₉ (A = Ba, Sr; B = W, Re), the substitution in the A- and B-site cations changed the octahedral rotation and distortion.