Designing new n=2 Sillen-Aurivillius phases by lattice-matched substitutions in the halide and [Bi 2Oc2] 2+ layer

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Australian Institute of Nuclear Science and Engineering (AINSE)
The chemical and structural flexibility of the perovskite structure, which makes is so ubiquitous in nature and useful in a range of technological applications, extends to layered variants such as Ruddleston-Popper, Dion-Jacobsen and Aurivillius phases. Multi-layered variants such as the Sillen-Aurivillius phases are related to Aurivillius phases by the insertion of an additional halide layer between every second [Bi2 02 2+ layer. Sillen-Aurivillius phases exist in various AnXm combinations, where n is the number of perovskite layers A and m the number of halide layers X. We have synthesised a new n=2 Sillen-Aurivillius compound Bi3 Sr2 Nb2 O11 Br based on Bi3 Pb2 Nb2 O11 Cl 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) in contrary to the belief of inserting a significantly larger halide layer in the new compound. We could not stabilise other combinations such as Bi3 Sr2 Nb2 O11 Cl and Bi3 Pb2 Nb2 O11 Br due to inter-layer mismatch. 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 a-b plane by 0.25 %, improving inter-layer compatibility with Br-. XANES analysis shows that the ferroelectric distortion of the B-site cation is less apparent in Bi3 Sr2 Nb2 O11 Br compared to Bi3 Pb2 Nb2 O11 Cl. Variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion.
Not available online. Conference Handbook is held by ANSTO Library at DDC 539.758/15
Crystal lattices, Perovskites, Layers, Halides, X-ray diffraction, Neutron diffraction
Liu, S., Blanchard, P. E. R., Avdeev, M., Kennedy, B.J. & Ling, C.D. (2013). Designing new n=2 Sillen-Aurivillius phases by lattice-matched substitutions in the halide and [Bi 2Oc2] 2+ layer. Paper presented at the 11th AINSE-ANBUG Neutron Scattering Symposium (AANSS), Sydney, 2 - 3 December 2013 (pp. 58)