Learning to control structure and properties of nano-scale ferroelectrics using defects

长期以来，铁电材料因其在存储设备、电容器和传感器等方面的应用而引起了广泛的技术兴趣。在改进现有设备的功能和开发高质量的新设备方面，成功依赖于实现对材料属性的更好控制，并最终实现按需定制的能力。这一建议的主要目的是研究原子尺度上的化学键特征、~5 nm尺度下铁电畴的结构和性质与~10-100 nm尺度下纳米铁电样品的总体尺寸和形状之间的相互作用。这些知识将为控制纳米级铁电体的性质提供巨大的机会，通过改变其化学组成，施加外场，将其暴露在紫外光下，塑造其结构，并应用盖层。我们将开发一种新的方法，用于纳米级铁电体的从头算原子模拟，并用于有效地分析磁区结构。这些方法将被应用于获得纳米级BaTiO_3中的磁畴的统计分布，并分析磁畴性质的分布与BaTiO_3纳米结构的尺寸和形状之间的相关性。在长度尺度的另一边，我们将研究氧空位的形成对磁畴结构的影响。我们将研究缺陷诱导性质的浓度依赖关系，并考虑到氧空位可以在几种电荷状态下存在。最后，我们将考虑含有缺陷的样品与外加电场的相互作用，并研究有限温度下的磁畴动力学。这些研究的结果将揭示点缺陷对纳米铁电材料性质的影响，并将提供通过控制缺陷的电荷态和改变其浓度来控制这些性质的机制。这些发现将促进表面探测方法的进一步发展，特别是在使用扫描隧道显微镜或原子力显微镜技术控制操纵表面原子方面。

Ferroelectric materials have long been of widespread technological interest for their applications in, for example, memory devices, capacitors, and sensors. Success in improving the functionality of existing devices and development of qualitatively new ones relies on achieving better control of the materials properties and, ultimately, the ability to tailor them on demand. The main aim of this proposal is to investigate the interplay between the character of the chemical bonding at the atomic scale, the structure and properties of the ferroelectric domains at ~5 nm scale and the overall size and shape of the nano-scale ferroelectric sample at ~10-100 nm scale. This knowledge would provide huge opportunities in controlling the properties of nano-scale ferroelectrics by changing their chemical composition, applying an external field, exposing them to ultra-violet light, shaping their structure and applying capping layers.We will develop a novel methodology for combined ab initio - atomistic modelling of nano-scale ferroelectrics and utilities for efficient analysis of the domain structure. These methods will be applied to obtain a statistical distribution of the domains in nano-scale BaTiO3 and to analyse the correlation between the distribution of the domain properties and the size and shape of the BaTiO3 nano-structures. On the other side of the length-scale, we will investigate the modification of the domain structure induced by the formation of oxygen vacancies. We will investigate the concentration-dependence of the defect-induced properties and take into account that oxygen vacancies can exist in several charge states. Finally, we will consider the interaction of the defect-containing samples with an external electric field and investigate the dynamics of the domains at finite temperatures. The results of these studies will reveal the effects of the point defects on the properties of nano-scale ferroelectrics and will provide mechanisms for controlling these properties by manipulating the charge states of the defects and by changing their concentrations. These findings will stimulate further developments in surface probe methods, particularly in the area of controlled manipulation surface atoms using scanning tunnelling microscopy or atomic force microscopy techniques.