Synthesis, structure and characterisation of the n=4 Aurivillius phase Bi5Ti3CrO15

The n=4 Aurivillius phase, Bi5Ti3CrO15, was synthesised by solid state reaction. Rietveld analysis of high resolution neutron diffraction data demonstrated this material to adopt the polar space group A21am at room temperature, transforming to the aristotype I4/mmm structure above 650 °C. This phase transition is coincident with an anomaly in DSC signal and relative permittivity, which are characteristic of a ferroelectric–paraelectric phase transition. Bi5Ti3CrO15 exhibits paramagnetic behaviour at low temperature, with short range antiferromagnetic interactions, but no evidence for long range magnetic ordering. This is considered a consequence of significant disorder of Ti and Cr over the available octahedral sites, as demonstrated by analysis of neutron diffraction data.

We report here the synthesis, structure and characterisation of the n=4 Aurivillius phase Bi5Ti3CrO15. Analysis of neutron powder diffraction and XANES data, supported by Madelung energy calculations, demonstrate partial ordering of Ti and Cr cations in the component perovskite layer. Bi5Ti3CrO15 is paramagnetic in the temperature range studied but exhibits a dielectric and DSC anomaly at 660 °C, characteristic of a ferroelectric–paraelectric phase transition. Analysis of high temperature neutron diffraction data confirm a direct phase transition between space groups A21am and I4/mmm at ∼660 °C.Figure optionsDownload as PowerPoint slide