A new layered bismuthate (Sr,K)(3)Bi2O7: Synthesis and crystal structure

A new layered bismuth-based mixed oxide with appropriate composition Sr1.5K 1.5Bi2O7 was synthesized at 300-450C and p(O-2) = 40 bar. This phase is the second member of the Ruddlesden-Popper series (Sr,K)(n=1)BinO3n+1. From X- ray powder diffraction, the structure was refined in the tetragonal space g roup I4/mmm with lattice constants a = 4.1549(1) Angstrom and c = 21.8273(6 ) Angstrom (Z = 2, R-I = 0.08, R-P = 0.066). However, electron diffraction patterns revealed the existence of additional weak reflections requiring a root 2a(p) x root 2a(p) x c unit cell to be indexed. No superconducting sig nal was detected to 1.5 K. (C) 1999 Academic Press.