Oxygen disorder phenomena in the modulated Bi₂Sr₂CoO₆-type structure

Abstract

The incommensurate modulated structure of Bi1.91Sr2CoO5.93 (a = 5.4614(6) Å, b = 5.4471(5) Å, c = 23.415(2) Å) with * = 0.240(2)*+* has been refined in the superspace group F2mm(01)00s using the four-dimensional formalism for modulated structures and single-crystal x-ray diffraction data. Two different regions with different sites for Bi and O atoms are evident along the modulation direction (called M and I regions). The oxygen disorder observed in the M region leads to different possible configurations for [BiO] layers. In particular, a double-chain configuration comparable to the one observed in related compounds is outlined. Therefore, a comparison with related compounds (BiCu or BiFe) is performed.