tuning between ground states and instabilities in layered perovskite-related materials

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Ferroelectrics, with macroscopic and switchable polarisation, and antiferroelectrics (with polar, ferroelectric state a little higher in energy than the non-polar ground state) are important for a wide range of applications. The origins of their polar or anti-polar behaviour include both electronic and geometric factors and can be described by both proper and improper mechanisms. Several families of layered perovskite-related materials have the potential to adopt polar structures by either proper or improper (specifically hybrid-improper) mechanisms and our project explores switching between these mechanisms to design new ferroelectric materials. The energy landscape for several known hybrid-improper ferroelectrics is more shallow than for related proper ferroelectrics and so we will investigate tuning between polar and anti-polar ground states in these hybrid-improper systems to design new antiferroelectrics.The project involves synthesis of layered perovskite-related materials and their structural characterisation by a range of techniques (including X-ray, neutron and electron diffraction and using Rietveld refinement). Physical property measurements will be carried out to understand structure - composition - property relationships in these systems. Experimental work will be complemented by computational studies to gain further insight into the balance between mechanisms that stabilise the ground states.