ORDERED PEROVSKITES CONTAINING PENTAVALENT BISMUTH - BA(BI0.75M0.25)3AND 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, o r Cu) have been synthesized under high oxygen pressure by using therma l decomposition of peroxides of Ba, Li, Na, or Sr in sealed platinum c apsules. The compounds have been characterized by X-ray diffraction, c hemical analysis, and infrared spectroscopy. X-ray diffraction studies showed that all the compounds have cubic perovskite-related structure s. Superlattice reflections due to the ordering of Bi5+ and M cations can be seen for all the compounds, except for BaBi0.66Cu0.33O3. The po wder X-ray diffraction patterns of Ba(Bi0.67M0.33)O3 phases were index ed in the space group Fm3m [(NH4)3FeF6 type], indicating a 1:1 orderin g between 1/2Bi5+ and (1/3M + 1/6Bi5+), while the superlattice reflect ions 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 struct ure. Such an ordering requires the structure to contain linear 180-deg rees Bi-O-Bi bonds along the a, b, and c axes, which is not a common f eature among the perovskite family of compounds. All the compounds, ex cept Ba(Bi0.67Cu0.33)O3, are electrical insulators with relatively hig h dielectric constants. The high electrical conductivity in the copper compound has been attributed to the presence of Bi in mixed valence s tates. (C) 1994 Academic Press, Inc.