Structural modulation in Bi2Sr2Ca0.4Y0.6Cu2O8+δ

• Published in: Journal of physics. Conference series Vol. 340; no. 1
• Main Authors: Beskrovnyy, A I, Jirák, Z
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 08.02.2012
• Subjects: Bismuth strontium calcium copper oxide; Bonding; Chains; Cuprates; Distortion; Flexing; Modulation; Neutron diffraction; Physics; Single crystals; Structural models; Superstructures; Symmetry; Yttrium
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/340/1/012055

The neutron diffraction study has been performed on a single crystal specimen of yttrium doped compound Bi2Sr2Ca0.4Y0.6Cu2O8+δ, which is a structural analog of the Bi-2212 superconducting cuprates. The average structure is orfhorhombic of Fmmm symmetry (a 5.448 Å, b 5.439 Å and c 30.416 Å). Two kinds of distortion are observed. The first one, manifested by satellite reflections of wavevector [τ,0,1] with τ 0.220, is associated with an incorporation of extra oxygen (δ∼0.44) into BiO bilayer. The respective modulation consists of a flexing of the bilayer and corrugation of other structural layers with period 4.5a. The second distortion is associated with displacements in the BiO planes due to Bi3+ bonding and lone pair ordering, which results in common cases in a formation of infinite ribbons of Bi-O-Bi- chains and decrease of average symmetry to Amaa. In the present system, the reflections characteristic for Amaa are absent and, instead, a diffuse scattering along the [001] direction is observed, pointing to a presence of 2-dimensional superstructure with in-plane period 9.0a – twice the one of the regular modulation. Based on these data, we propose a structural model in which bonding chains in the BiO planes of Bi2Sr2Ca0.4Y0.6Cu2O8.44 are segmented and rearranged in a tweed pattern.