Ferroelectric materials are technologically important (with applications including non-volatile memory devices and capacitors) but the origin of their reversible polarisation is also of academic interest. In tradition “proper” ferroelectrics, the paraelectric – ferroelectric phase transition on cooling is driven by the polar displacement of cations relative to anions, and is often associated with the electronic structure of particular cations (e.g. the “inert pair” 6s 2 cations Bi 3+ , Pb 2+ , or d 0 transition metals). The field has been shaken recently by the discovery of “hybrid-improper” mechanisms to give ferroelectricity, in which other non-polar structural changes combine to lower the symmetry to that compatible with ferroelectricity 1 (and other acentric properties e.g. piezoelectricity, pyroelectricity). This research is still at an early stage but opens the possibility of preparing new classes of ferroelectrics (and related polar materials). Recent work has highlighted the potential for the layered materials to show such properties arising from “hybrid-improper” mechanisms. 2 I’d like to present some of our recent work on Dion-Jacobson phases investigating the balance between these two mechanisms and possibilities to tune the properties of these materials. 3-4
1. Bousquet, E.; Dawber, M.; Stucki, N.; Lichtensteiger, C.; Hermet, P.; Gariglio, S.; Triscone, J.-M.; Ghosez, P., Nature 2008, 452, 732-736.
2. Benedek, N. A.; Rondinelli, J. M.; Djani, H.; Ghosez, P.; Lightfoot, P., Dalton Trans. 2015, 44, 10543-10558.
3. Robinson, E. J.; Patrick, S. J.; Bousquet, E.; Levin, I.; Stennett, M. C.; Hyatt, N. C.; Tran, T. T.; Halasyamani, P. S.; McCabe, E. E., in preparation 2017.
4. McCabe, E. E.; Bousquet, E.; Stockdale, C. P. J.; Deacon, C. A.; Tran, T. T.; Halasyamani, P. S.; Stennett, M. C.; Hyatt, N. C., Chem. Mater. 2015, 27, 8298.
University of Kent