Designing new n=2 Sillen–Aurivillius phases by lattice-matched substitutions in the halide and [Bi2O2]2+ layers

• A new Sillen–Aurivillius phase Bi3Sr2Nb2O11Br is synthesised based on Bi3Pb2Nb2O11Cl.
• The stacking axis contracts although local expansion accommodates the larger halide Br.
• Majority of the contraction is observed in the [Bi2O2]2+ layers where we replaced Pb2+ for Sr2+.
• Removing the Pb2+ lowers the lone pair effect and improves inter-layer compatibility.
• XANES and NPD suggest that the ferroelectric properties are minimised or suppressed.

A new n=2 Sillen–Aurivillius compound Bi3Sr2Nb2O11Br has been synthesised based on Bi3Pb2Nb2O11Cl by simultaneously replacing Pb2+ with Sr2+ and Cl− with Br−. Rietveld refinements against X-ray and neutron powder diffraction data revealed a significant relative compression in the stacking axis (c-axis) of the new compound. Sr2+ doping reduces the impact of the stereochemically active 6s2 lone pair found on Pb2+ and Bi3+, resulting in a contraction of the c-axis by 1.22% and an expansion of the ab plane by 0.25%. This improves the inter-layer compatibility with the larger halide Br−. Analysis of X-ray absorption near-edge spectroscopy data show that the ferroelectric distortion of the B-site cation is less apparent in Bi3Sr2Nb2O11Br compared to Bi3Pb2Nb2O11Cl, and variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion.

The structural expansion and contractions in the stacking axis of co-doped Sillen–Aurivillius phases.Figure optionsDownload as PowerPoint slide