ORDERED PEROVSKITES CONTAINING PENTAVALENT BISMUTH - BA(BI0.75M0.25)3 AND BA(BI0.67M0.33)O3

New Bi5+-containing perovskites of the types Ba(Bi0.75(5+)M0.25(1+)O3 (M = Li or Na) and Ba(Bi0.67(5+)M0.33(2+)O3 (M = Mg, Ca, Sr, Ba, Cd, or Cu) have been synthesized under high oxygen pressure by using thermal decomposition of peroxides of Ba, Li, Na, or Sr in sealed platinum capsules. The compounds have been characterized by X-ray diffraction, chemical analysis, and infrared spectroscopy. X-ray diffraction studies showed that all the compounds have cubic perovskite-related structures. Superlattice reflections due to the ordering of Bi5+ and M cations can be seen for all the compounds, except for BaBi0.66Cu0.33O3. The powder X-ray diffraction patterns of Ba(Bi0.67M0.33)O3 phases were indexed in the space group Fm3m [(NH4)3FeF6 type], indicating a 1:1 ordering between 1/2Bi5+ and (1/3M + 1/6Bi5+), while the superlattice reflections seen in the X-ray data for Ba(Bi0.75Na0.25)O3 and Ba(Bi0.75Li0.25)O3 were indexed in the space group Im3m, indicating a 1:3 long-range order of M1+ and Bi5+ ions at the B site of the ABO3 perovskite structure. Such an ordering requires the structure to contain linear 180-degrees Bi-O-Bi bonds along the a, b, and c axes, which is not a common feature among the perovskite family of compounds. All the compounds, except Ba(Bi0.67Cu0.33)O3, are electrical insulators with relatively high dielectric constants. The high electrical conductivity in the copper compound has been attributed to the presence of Bi in mixed valence states. (C) 1994 Academic Press, Inc.