标题： 铅钛酸盐和锶钛酸盐单层和双层中的多形性和铁电性的化学控制 显示英文标题

标题： Chemical control of polymorphism and ferroelectricity in PbTiO3 and SrTiO3 monolayers and bilayers

摘要： 钙钛矿层存在于三维材料、二维异质结构和纳米管中，通常从高对称性扭曲以促进可应用于许多应用的偶极极化。 使用密度泛函理论计算，显示二维材料PbTiO3和SrTiO3双层中的铁电性由键的断裂和形成过程控制，这些过程作为二进制开关。 这些堆叠依赖的过程随着从高对称结构的松弛和双轴应变的应用而开启和关闭，它们的协同重排导致铁电极化切换的低能垒。 识别出介于高对称八面体形式和低对称铁电形式之间的对称性中间结构，从而能够识别与传统“铁畸变”和“反铁畸变”TiO6八面体变形相关的固有过程。 显示铁畸变模式是由同时应用两种不同类型的曲线反铁畸变运动产生的。 通过协同的化学键的形成和断裂，这四种角度变量控制极化切换。 这些细微之处使得极化对化学环境和温度效应敏感，这些效应可以操纵应变和结构，在未来设备中具有可利用的特性。 显示英文摘要

摘要： Layers of perovskites, found in 3D materials, 2D heterostructures, and nanotubes, often distort from high symmetry to facilitate dipole polarisation that is exploitable in many applications. Using density-functional theory calculations, ferroelectricity in bilayers of the 2D materials PbTiO3 and SrTiO3 is shown to be controlled by bond breakage and formation processes that act as binary switches. These stacking-dependent processes turn on and off as a function of relaxation from high-symmetry structures and the application of biaxial strain, and their concerted rearrangements lead to low energy barriers for ferroelectric polarisation switching. Structures with symmetry intermediate between high-symmetry octahedral forms and low-symmetry ferroelectric forms are identified, allowing the intrinsic processes associated with traditional "ferrodistortive" and "antiferrodistortive" distortions of TiO6 octahedra to be identified. Ferrodistortive-mode activity is shown to be generated by the simultaneous application of two different types of curvilinear antiferrodistortive motions. In this way, four angular variabes control polarisation switching through the concerted making and breaking of chemical bonds. These subltities make the polarisation sensitive to chemical-environment and temperature effects that manipulate strain and structure, features exploitable in futuristic devices.