Single crystal and HREM study of the “Bi-Sr” stabilized BaMnO3 9R polytype

Single crystals of the BaMnO3 9R polytype were grown at normal pressure. Their EDS analysis shows that they are bismuth doped (less than 3% per Mn atom), which is in agreement with their black color. The accurate structure was determined from a single crystal X-ray diffraction study. The rhombohedral lattice, referred to as the related hexagonal axes (a = 5.663(1) Å and c = 20.995(3) Å) and the space group R3̄m are consistent with the (hhc)3 close packed layers stacking sequence. No evidence of oxygen vacancies, with respect to the “O3” stoichiometry, was detected, and the stacking defects checked from HREM investigations revealed that the 9R stacking is established very regularly over wide areas.