SINGLE-CRYSTAL AND HREM STUDY OF THE BISR STABILIZED BAMNO3 9R POLYTYPE

Single crystals of the BaMnO3 9R polytype were grown at normal pressur e. Their EDS analysis shows that they are bismuth doped (less than 3% per Mn atom), which is in agreement with their black color. The accura te structure was determined from a single crystal X-ray diffraction st udy. The rhombohedral lattice, referred to as the related hexagonal ax es (a = 5.663(1) Angstrom and c = 20.995(3) Angstrom) and the space gr oup R (3) over bar m are consistent with the (hhc)(3) close packed lay ers stacking sequence. No evidence of oxygen vacancies, with respect t o the ''O3'' stoichiometry, was detected, and the stacking defects che cked from HREM investigations revealed that the 9R stacking is establi shed very regularly over wide areas.