Structural relationships between 2D and 3D Ba–Mn oxides

Ba4Mn3O10 and Ba6Mn5O15 constitute the n=3 and n=5 terms of a new layered Ban+1MnnO3n+1 family, consisting of n 2H-ABO3 hexagonal perovskite-like blocks separated by a BaO layer. The structural essential feature is the presence of zig-zag layers perpendicular to [010] separated by Ba atoms and folded along c-axis. The layers are built up from (Mn3O12) units constituted by three (n=3) and five (n=5) octahedra sharing faces connected via their apices by sharing two of their three terminal corners at each end of the (Mn3O12) group. These layered phases are structurally related to the 9R and 15R Ba–Mn hexagonal polytypes since they can be derived by the insertion of BaO layers into the structural framework of the corresponding hexagonal polytype.