SYNTHESIS, SINGLE-CRYSTAL GROWTH AND STRUCTURAL CHARACTERIZATION OF THE NEW LAYERED PEROVSKITE BA2CU0.5NA0.5CO5

A new layered perovskite compound Ba-2(Cu0.5Na0.5)CO5 has been synthes ised in the form of a pure sintered polycrystal and crystals of sub mi llimetre size that have been grown by solidification of stoichiometric melts. The structure corresponds to a distorted double perovskite wit h a tetragonal cell (s.g. P4/mmm, a=4.135(1), c=7.712(1) Angstrom) wit h alternating (Cu,Na)-O-2 and C-O-2 planes. The refinement of the atom ic occupancies confirms the results of oxygen and carbon estimations a nd indicates that the average valence of the Cu ions must be close to 3. In the structural model we propose, the material lias a domain stru cture determined by the occurrence of exchange disorder in the cation sequence of the Cu,Na-O-2 planes.