Crystallographic shear mechanisms in Rh one-dimensional oxides

Electron diffraction and high resolution electron microscopy have been used to characterize two new one-dimensional superstructures in the ARhO system (A = Ca, Sr) related to the 2H-ABO3-type. They are formed by the intergrowth of n A3A′BO6 blocks, showing the Sr4RhO6-type, with A12A′2B8O30 blocks, constituted by two A3O9 and two A3A′O6 layers alternating in the stacking sequence 1:1, leading to the A27A′7B13O60 (n=5) and A30A′8B14O66 (n=6) compositions. A crystallographic shear mechanism is proposed to describe the structural relationship between Sr4RhO6 (A3A′BO6-type) and the new superstructures.