Oxygen disorder phenomena in the modulated Bi2Sr2CoO6-type structure

The incommensurate modulated structure of Bi_1.91Sr₂CoO_5.93 (a = 5.4614(6) Å, b = 5.4471(5) Å, c = 23.415(2) Å) with icons/Journals/Common/vecq" ALT="vecq" ALIGN="TOP"/>^* = 0.240(2)icons/Journals/Common/vecb" ALT="vecb" ALIGN="TOP"/>^*+icons/Journals/Common/vecc" ALT="vecc" ALIGN="TOP"/>^* has been refined in the superspace group F2mm(0icons/Journals/Common/beta" ALT="beta" ALIGN="TOP"/>1)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.