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

具有宏观和可切换极化的铁电体和反铁电体（具有比非极性基态能量稍高的极性铁电体状态）对于广泛的应用是重要的。它们的极性或反极性行为的起源包括电子和几何因素，并且可以通过适当和不适当的机制来描述。层状钙钛矿相关材料的几个家庭有可能通过适当或不适当（特别是混合不适当）机制采用极性结构，我们的项目探索了这些机制之间的切换，以设计新的铁电材料。几种已知的杂化反常铁电体的能量分布比相关的正常铁电体更浅，因此我们将研究这些杂化反常系统中极性和反极性基态之间的调谐，以设计新的反铁电体。该项目涉及层状钙钛矿相关材料的合成及其结构表征，通过一系列技术（包括X射线、中子和电子衍射，并使用Rietveld精化）。将进行物理性质测量以了解这些系统中的结构-组成-性质关系。实验工作将通过计算研究来补充，以进一步了解稳定基态的机制之间的平衡。

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.