The crystal and defect structures of polar KBiNb2O7

Subhadip Mallick, Weiguo Zhang, Maria Batuk, Alexandra S. Gibbs, Joke Hadermann, P. Shiv Halasyamani, Michael A. Hayward*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

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.

Original languageEnglish
Pages (from-to)1866-1873
Number of pages8
JournalDalton Transactions
Volume51
Issue number5
Early online date5 Jan 2022
DOIs
Publication statusPublished - 7 Feb 2022

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