The crystal and defect structures of polar KBiNb2O7

Journal article

KBiNb2O7 was prepared from RbBiNb2O7 by a sequence of cation exchange reactions which first convert RbBiNb2O7 to LiBiNb2O7, before KBiNb2O7 is formed by a further K-for-Li cation exchange. A combination of neutron, synchrotron X-ray and electron diffraction data reveal that KBiNb2O7 adopts a polar, layered, perovskite structure (space group A11m) in which the BiNb2O7 layers are stacked in a (0, ½, z) arrangement, with the K+ cations located in half of the available 10-coordinate interlayer cation sites. The inversion symmetry of the phase is broken by a large displacement of the Bi3+ cations parallel to the y-axis. HAADF-STEM images reveal that KBiNb2O7 exhibits frequent stacking faults which convert the (0, ½, z) layer stacking to (½, 0, z) stacking and vice versa, essentially switching the x- and y-axes of the material. By fitting the complex diffraction peak shape of the SXRD data collected from KBiNb2O7 it is estimated that each layer has approximately a 9% chance of being defective – a high level which is attributed to the lack of cooperative NbO6 tilting in the material, which limits the lattice strain associated with each fault.

Authors: Mallick, S; Zhang, W; Batuk, M; Gibbs, AS; Hadermann, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Royal Society of Chemistry
• Journal: Dalton Transactions
• Volume: 51
• Issue: 5
• Pages: 1866-1873
• Place of publication: England
• Publication date: 2022-01-05
• Acceptance date: 2022-01-05
• DOI: 10.1039/d1dt04064b
• EISSN: 1477-9234
• ISSN: 1477-9226
• Pmid: 35018920
• Language: English
• Keywords: FFR