Synthesis and Characterization of New Phases: Sr3.75K1.75Bi3O12 and Sr3.1Na2.9Bi3O12

New hexagonal phases were found in the Sr-K(Na)-Bi-O systems and characterized by X-ray powder diffraction, electron diffraction, and high-resolution electron microscopy (HREM). The crystal structures of Sr3.75K1.75Bi3O12 (space group P 2m, a=10.4434(1) ?, c=3.37932(4) ?, RI=0.019, RP=0.055) and Sr3.1Na2.9Bi3O12 (space group P 2m, a=10.1102(4) ?, c=3.3389(1) ?, RI=0.024, RP=0.070) were refined using X-ray powder data. The structures consist of chains of BiO6 octahedra linked by the common edges whereas A cations occupy the interstices between the chains. This structure can be considered as the end member of the new (Sr, K)6n+2Bi3n-3O12n homologous series found by electron microscopy. The homologues with n=4, 5, and 6 were observed, and their structures were deduced from HREM observations.