A Strontium-Rich 2201-Type Cobaltite with a Nonmodulated Structure: Bi1−xSr3+xCoO6−δ

Abstract A strontium-rich 2201-type oxide, Bi 1− x Sr 3+ x CoO 6− δ , with a nonmodulated structure has been synthesized. X-ray powder diffraction and high-resolution electron microscopy show a 1:1 ordering of Bi 3+ and Sr 2+ species within the two intermediate [Bi 0.5 Sr 0.5 O] ∞ layers. The distorted [CoO 2 ] ∞ layers can also be described as built up from CoO 6 octahedra and CoO 5 pyramids, stacked along a alternately. In this structure, Bi 3+ exhibits a tetrahedral coordination BiO 3 L , taking into consideration its 6 s 2 lone pair denoted L . The magnetic behavior of this trivalent cobalt oxide suggests that this species is not purely high spin and shows an antiferromagnetic transition below 50 K, similar to that observed in the tubular cobaltite.