Fig. 1: Distinct polytypes of hexagonal-perovskite barium iridates.
Three polytypes, a 9R, b 6H, and c 12R, are presented. As indicated by black arrows in the illustrations in the left-hand column, each [IrO6] octahedron is face-sharing in the [Ir2O9] dimers of the 6H polytype and in the [Ir3O12] trimer in the 9R and 12R polytypes. Co, Ni, In, Nb, and Ta occupy the specific sites bridging the two adjacent dimers or trimers, whereas Mn distributes randomly in the lattice.
