Electron diffraction and high-resolution electron microscopic studies showed that non-stoichiometry in BaMnO3-x perovskite-type materials, where x was between 0.22 and 0.40, was accommodated either by disordered inter-growths of hexagonal BaMnO3 polytypes when x was between 0.22 and 0.25, or by a random distribution of anionic vacancies when x was between 0.25 and 0.40. When x was equal to 0.25, an ordered 4H-Ba4Mn4O11 phase was obtained with the stacking sequence: ... hchc .... Structural models were considered which showed ordering of the vacancies along the cubic layer.

M.Parras, J.Alonso, J.M.González-Calbet, M.Vallet-Regí: Journal of Solid State Chemistry, 1995, 117[1], 21-9