ملخص: Single crystals of the new Ba4Mn2NaO9 have been prepared by electrosynthesis in molten NaOH. Its crystal structure has been solved from XRD data (a=10.006(2), c=8.210(3), space group P321, Z=3, R=3.21%, wR=3.52%). It belongs to the wide family of 2H-related perovskite materials and shows columns of face-sharing MnO6 octahedra and NaO6 prisms according to the -(oct-oct-prism)- sequence isolated by Ba2+ cations. The main characteristic of this new oxide is its mixed Mn4+/Mn5+ valence rarely reported up today. Help to the superspace formalism, Ba4Mn2NaO9 (or Ba1+xNaxMn1-xO3 with x=1/3) can be regarded as composed of two interpenetrating sublattices [Ba1+x] and [Na1/3Mn2/3O3] with their own period along the c axis. The ratio [gamma] of these two periods is rational [gamma]=c1/c2=2/3. This composite structure approach which allows us, help to established rules, to predict the crystal structure from the [gamma]-only knowledge has also been pointed out in this work.

لغة: إنجليزية